Yeah, this hasn't been a problem since forever (or at least I haven't noticed). They had to break the undo file format a while ago to actually work correctly for byte-level buffer change events (very important for tree sitter and other plugins listening for buffer changes). The undo file format is versioned, too, so it's not just YOLO'd; Neovim has since forever returned an error saying there's a version incompatibility. The outrage here doesn't make a lot of sense to me.

The original author of this post (on Mastodon) appears to have a bone to pick with Neovim since it's "platforming white supremacists"? I couldn't figure out what this meant. Some sort of internet drama I guess.