Hi, I was in the raid 25, and i have drop fps(jump fps /freezing in fight), i disable all addon except Ndui, but fps drop again, after disable UI fps is fine.
it happens only in Raid 25 or 20+player in party!! small bg/dungers/raid 10 and other its fine!
i tried elvui/kkthnx , elvui dont drop fps but kkthnx have the same problem, are similar, maybe you know what the problem

No idea. I don't play classic at all, no way to test it atm.
You might try to disable different modules in NDui and see which part might cause the fps drop.