Better Third Person is weird behind the scenes! It seems to have its own camera system which it forces Minecraft to render from the view of while it fiddles with the default camera to rotate the player entity, which screws up a lot of mods that rely on the camera orientation. It's also closed source (ew!!!) so implementing compatibility might be difficult.

@PieKing1215 can this at least be acknowledged?

Sorry I haven't really looked into this much, it's been kinda low priority since it being closed source makes it way harder to fix.
I'll probably get around to it someday but there's only so much I can do without being able to see their code.

There's only so much I can do without being able to see their code.

try https://www.decompiler.com

I know decompilers exist but decompiling closed source mods and referencing their code is kinda looked down upon and also legally questionable, so it's kinda out of the question for me (unless I ask the dev and they give me explicit permission)

Fixed in v0.9.0 (also on Modrinth)