do you have an AMD gpu (either dedicated or laptop integrated)?
with 3.4.2 we got some updates from the latest Dragonflight client and there are tons of reports on Blizz forum about AMD cards not interacting properly with the 10.1 Dragonflight client, especially on DX12. switching to DX11 solved it for most people but resulted in a bit worse performance (lower fps mostly).
not the exact same issue, but prior to the 3.4.2 update today, for around 3 weeks I had error #139, resulting in some weird shader glitches on the character selection screen.bunch of testing, diagnostics, reinstalls, DX11 setting, cache clearing, eventually full windows reinstall didn’t resolve. I narrowed it down to my AMD igpu (my laptop has no mux switch, so the integrated graphics are always in use).
however I only experienced this before 3.4.2 - probably one of the many WotLK hotfixes/small updates in the past month included preliminary assets from the DF client that messed up my graphics and got only fixed once P3 actually going live.
https://www.reddit.com/r/classicwow/comments/14f2t8w/error_132_after_patch_342/
Все же там прилетало обновление клиента до DF и меня не поглючело.