Winning wasn't what Felix hoped it would be.
Even though Felix didn't get the ladybug and cat miraculous in "Emotion", he still accomplished what he set out to do, he defeated the heroes and used his own power to transform the world into what he wanted it to be, regardless of not getting a wish from the miraculous. Felix got what he wanted, only to realize he became everything he hated.
Felix's goals have always revolved around the peacock miraculous, however, the deeper he got in his mission to obtain the very jewel that controlled his entire existence, the more he uncovered secrets that left him resentful towards the people in his life and the world around him.
Felix resented Gabriel for not only keeping secrets he and his mom had a right to know (more here), but for also making the careless decision to entrust the peacocks power to his father, Colt, of all people.
It was no coincidence Felix looked like Adrien, and with Colt's death having been revealed in "Felix", it was obvious his death was a direct result using the peacock miraculous to bring to life a son that looked like Gabriel's. Anyone who used the peacock's power in its broken state was doomed to die from it. The jewel alone remained within the Agreste family, no one but the people closest to them would know about its power, Colt being one of them. Unfortunately, for much of Felix's life, people thought his dad was keeping him out of trouble, meaning that before Colt's death, Felix was well known for being a very obedient son, but this was far from the truth.
Felix's lack of grief over Colt's death implied he had a deep hatred for his dad and for good reason, Colt possessed the ring that contained Felix's amok, but he abused the power he had over Felix and Felix knew Gabriel was the same way towards Adrien, worse yet, he later learned it was the same for Kagami and her family (more here).
With Colt gone, and his fathers ring now in his possession, Felix was shown to be willing to be extremely defiant to those around him after years of being restrained by his father from being who he wanted to be, leaving him willing to do anything he could if it meant he could get what he wanted, regardless of the consequences it would bring onto others.
Kagami and Adrien also had a strong desire to break away from their parents control, but were more secretive about wanting to do so, because unlike Felix, the fear of disappointing their parents expectations was still there to keep them in line. However, this didn't stop Felix from attempting to make the two question how unnatural it was for them to obey.
(Back in "Felix", Felix questions Adrien's willingness to obey all of Gabriel's orders.)
(In "Emotion", Felix questioned Kagami if she was truly as free as she claimed, she wasn't.)
Felix might have been freed from his fathers control, and later became successful in re-obtaining the peacock miraculous, but there were still obstacles preventing him from obtaining what he believed was a true sense of freedom in the world, not just for himself but for everyone he felt never had the right to take control of their own lives. With the threat of people like Colt still present in the world, such as Gabriel and Tomoe, Felix was convinced he alone had to bear the responsibility of freeing anyone who was still under the control of others. But as it turns out, Felix's desire for freedom ran a lot deeper than anyone realized.
In "Emotion", when Marinette told Felix how unsettling it was to see everyone at the Diamonds Dance look at her like she was some kind of monster who was unfit to live among them, a nerve was struck, enough to make Felix drop his Adrien act at the dance.
Felix knew the feeling Marinette was experiencing, because he had experienced it every day of his life. Felix might have been created from the peacock's power to be just as human as everyone else, but the look on his face as he heard Marinette talk about how the people of high status within the room felt they were entitled to decided who should and shouldn't be a monster among them, brought him back to the one person who made him feel like he would forever be excluded from humanity, his father.
To know the kind of control another person could have over another living being, especially a senti like him, was enough to leave Felix with the conclusion that if he couldn't be part of the world without being looked at as a monster, then perhaps it was the world that had to be transformed to be fit for those who had just as much right to decide their own future, without fear of being looked at as a thing that needed to be controlled and wiped from existence by those who felt they were entitled to do so.
Felix did some terrible things to get to where he needed to be in "Emotion", but regardless of what he did, he truly believed that everything he did to create a free world, he did for the sake of the people he cared about. However, his hopes and dreams quickly turned into delusions blinding him from seeing that he was destroying everything he swore to bring everyone in his life.
Regardless of how unhappy Kagami and Adrien were over Felix's plans to wipe out everyone, including the people they loved, who stood in his way of creating his ideal world for them, Felix genuinely thought they would come around to seeing the good in his gift to them. For the first time in their entire lives, they were free, and anyone who posed a threat to control them again, friends and family alike, were now gone. If they needed something or someone to feel happy in their new world, he could easily give it to them, like Marinette, who proved to Felix she only wanted to support Adrien's efforts in deciding what was best for himself and had no intentions of controlling him like Gabriel did. However, what changed everything Felix believed was well within his control, was Marinette's disappearance.
Felix was successful in his plans, but the one thing that made it all come crashing down, was fear over his own power. To Felix, people like Gabriel, Tomoe and Colt were the real monsters of the world who had to disappear, but as Felix panicked in "Emotion" the more he believed he couldn't bring back Marinette, he grew terrified the more he realized he really did do the one thing only a monster like his father would do, he misused his power and snapped another living being out of existence in a fit of anger, with no way of bringing them back. In an instant, Felix realized he really was becoming no different than Monarch( Gabriel), than Tomoe, and to his horror, his own father.
In the midst of believing he was not in control of himself and the immense power he had, power that allowed him to decide who could and couldn't exist, Felix thought back to what he told Ladybug, he said there was no price too high for him to pay in his pursuit of a free world, as he had nothing left to lose, but he did.
It was easy enough to disregard anyone who posed a sense of authority against him, but there was Adrien and Kagami, the two people in his life who shared his struggle as a sentibeing, calling him the monster among them, desperate to stop his plans.
Felix won, but now, in order to keep that victory, he would have to be willing to snap away the very people in his life he wanted to help, just as he did with the rest of humanity in Paris, but was he willing to do it? No, he wasn't.
(Felix explains that he never meant to hurt Adrien and Kagami, he only wanted to give them what he felt they had a right to have, a life where they were free to decide their own future)
Ladybug said winning isn't always what you think it is. Felix wanted a world where no one would be controlled, and he got it, but now, it was he who was in control of everyone else, deciding who could and couldn't exist in the world depending on whether or not they would stand against him, stand against what he believed was right and wrong.
(Felix made everyone who fought against him disappear with the snap of his fingers the moment the light of his red moon touched them)
Felix had hoped that in his world, no one would be excluded like he was, everyone would be free and happy and accepted now that the people who excluded them were gone. But now, everyone would only be as happy and free as he would let them, anyone else he believed was unfit to be part of his world, were in the end excluded, regardless of posing no actual harm to him or the people he cared about.
Felix wanted everyone in his world to be free to decide their own future. However, by denying Adrien and Kagami their choice to live a future alongside the people they cared about, people like Marinette, it was he who was now keeping everyone from living the life they wanted to choose for themselves, just as his father once did to him.
And rather than create his senti brethren out of a greater sense of compassion towards them, he created his first sister, the red moon, out of a deep rooted hatred for others, just like his father did when he used the peacocks power to create him(more later). Everything Felix did, he thought he did for the sake of freedom, but amidst all that he planned, it felt more and more like Felix found himself doing everything he could for the sake of finally being the one who was in control, after a lifetime of being someone else's puppet.
Felix said he wanted everyone to be free to decide their own future, to be free to be who they wanted to be, but out of everything he ever wanted to be, he never wanted to believe he was a monster. Felix told Ladybug there was no price too high for him in his pursuit of creating a free world, but if the price of that free word meant he had to be every bit the monster his father was, someone he likely swore never to become, then he would rather give up the world he won, and he did.
(Felix returns all of humanity and snaps the red moon out of existence, giving up on creating a free world and choosing to risk returning to a life in a world where he could lose his freedom all over again. Winning was not worth become the monster his father was. )
