Thanks, I have some more proposed changes/fixes at https://gitlab.winehq.org/afrantzis/wine/-/commits/wip/wayland-buffer-queue .
This MR effectively makes `wp_viewport` a requirement for the Wayland driver, even for non-scaled scenarios, so I would say let's check for it at startup like we do with other protocols and remove further runtime checks (can be done in a follow-up MR).