Go test this image https://chewitt.libreelec.tv/testing/LibreE…-12.90.1.img.gz and report back. Note that this image is LE13 and we switched Generic from OpenGL back to OpenGLES so if you have screensaver and visualisation add-on installed those will need to be removed, the cache in /storage/.kodi/addons/cache deleted, and then the add-on needs to be reinstalled else things will crash. Just leave settings present and it's no big deal.
NB: I'm not answering the Q's above as there are known rendering bugs solved and notable changes to rendering in this image; and the combination means triaging anything on LE12.2 isn't a productive use of time (there are no plans for a 12.3 release).