So this gets into a lot of discourse over whether polyamory is an orientation or simply a relationship structure you can pursue. (I think both are valid and vary from person to person.)
Ignoring that discourse and focusing on what you are asking me, ambiamory is basically a sub-identifier that falls under the polyamory umbrella used for people who are fine with either mono or polyam relationships. They feel no particular need to pursue either, and it causes them no distress to be in either situation.
This is in contrast to some polyamorous people who could not and would never consider monogamy because it would feel like denying a part of themselves and leave them feeling trapped and unfulfilled.
Similarly, some monogamous people cannot tolerate polyamory because it's not how they are wired. They can do all the therapy, follow all the steps, do everything "right," and still feel like something is majorly wrong and distressing.
And that's fine. Polyamory isn't for everyone, just like monogamy isn't for everyone.
These "one or the other" attitudes can be very prevalent in both polyam and mono spaces. For some of us, however, that you have to pick a side is uncomfortable, and feels like we're being shoved into boxes that don't fit.
That's where ambiamory comes in.
So yes, there are some polyamorous people who are fine with just one partner and can feel polysaturated at one partner due to life or other issues, but it's up to them whether they want to use the term ambiamory.
Some people would get quite annoyed if you called them ambiamorous instead of polyamorous because while they might be functionally monogamous at that moment, they do not identify with monogamy on a personal level. And again, that's fine.
The problem we're currently seeing in the community is people who take this view to an extreme and are now calling ambiamorous people interlopers and calling our interest in polyamory a "phase," implying that we're just using polyamorous people to experiment before reverting to monogamy when we find "the one."
It's classic binary "pick a side" discourse, and I'm over it.