There’s a long-running thread about this in the tech support forum (it started nearly a year ago). Take a minute to read through it and see if it’s similar to what you’re dealing with: Black box textures/animations in some acts
I’ve been hyper-focused on this and the Shenk crash this week. I think I solved it for myself, so I posted a detailed explanation in that same thread: Black box textures/animations in some acts - #58 by cristobal03-1793 - Technical Support - Diablo 2 Resurrected Forums
That might help you? gl