About SuperTuxKart
I tried to install manually SuperTuxKart on my Raspberry Pi 4b, your script wasn't working ("segmentation fault" in xorg logs related to the source-compiled driver from your script) so I installed SteamLink (which installs xorg, I didn't want to install it manually to not break anything) then installed supertuxkart apt package then xinit supertuxkart.
It worked really smoothly even with graphical parameters at maximum. Only thing that wasn't working was audio (maybe because of a xorg config).
Could you please reconsider adding STK to RetroPie-Extra and rework the script to make it working?
PS : SuperTuxKart v1.2 is out, can you add a way to install either from source or the precompiled binary from the official website instead of using the outdated one in Raspbian repos (v0.9!) ?