Then I guess it could be a vram problem? Same res, no res scaling, 3090, no performance problems. Yes, the 90 is a bit faster but not much. But a lot more vram.
Weird that you stopped at these 3 bosses. They are the best in ds3. Midir is just a great big boss fight, same as Gael who is the proto souls fight and halflight was great when the game had lots of players online; don't know how it is offline or pve only.
My dude, as someone from the early 90s internet myself that's not new tangled speech, that's old af and from text forums and Usenet threads.