It also sounds like fullscreen direct scanout might have worked in jammy but doesn't in noble. You can test that theory by comparing the windowed performance between jammy and noble. Or by checking the scanout method using MUTTER_DEBUG=kms and grepping the log for "Post" (Wayland only though).
It also sounds like fullscreen direct scanout might have worked in jammy but doesn't in noble. You can test that theory by comparing the windowed performance between jammy and noble. Or by checking the scanout method using MUTTER_DEBUG=kms and grepping the log for "Post" (Wayland only though).