I saw the following post, and I wanted to ask you how true that is: "The Strong boys' death is the curse of Harrenhall; all the families that are the lords of Harrenhall, their line ends."
I think you forgot to add the link to said post? I will answer what you gave here, though.
I don't know about a person or living, self-conscious entity necessarily cursed Harrenhal and all its people, but I could believe that the misery and rage from the Hoare's slave exploitation of the Riverlanders (I mean prisoners of battles and smallfolk) left an "impression" powerful enough to become an epicenter or magnet (bc we know magic and gods exist) for tragedy...OR anyone who has Harrenhal was always a house that was in the eye of every other house for the potential the lands and castle could bring. IDK.
The "curse" predates the Strongs; the first house who ruled/was granted Harrenhal was the House Qoherys (Gargon the Guest was killed during a rebellion), then it was the Harroways, then it was the Towers house. Then Maegor Towers & Rhaena (Alysanne's sister)'s died, and Jaehaerys gave Harrenhal to the Strongs.
2 out of the 3 houses mentioned before the Strongs ended with terrible violence, so yes there was a cultural sense in Westeros that any house that takes up Harrenhal as their new seat their line will die very shortly, not even last 4 generations. The castle itself is and has never been fully restored to its short-lived prior completion before Aegon/Balerion burned it and its Hoare inhabitants alive.
Oh, and what "boys"? Because Rhaenyra's sons?--if that post was sneering, then I'd dismiss that since the boys were not in any way a part of the Strong house or lineage ever since they were given the surname Velaryon and claimed/never revealed in the first place. That's them holding onto an ideological identity rather than a legal one so they can feel satisfied with hating or delegitimizing Rhaenyra's claim or theirs. People can be very weird when it comes to those born out of wedlock both when they are reading these books and when they're just out and about.