I was able to successfully build for a RPi4 from your dev-RR branch. 😀
The system booted to Kodi successfully. The default of 4Kp30 display setting seemed a bit glitchy and sluggish. I tried changing to 1080p60 but it was only displaying as the upper left quarter of the screen. I tried to start emulationstation and retroarch from the home screen and both relaunched Kodi (I'm guessing both crashed and your script/systemd relaunched Kodi).
To see if these were LE issues or just your build I reflashed the SD card with the current 9.2 beta (9.1.501). The default of 4Kp30 did not feel sluggish and changing to 1080p60 did not result in only the upper left corner display.
I didn't pull logs yet but want to give you a heads up on a couple early issues. Hopefully I can review more this weekend and get some logs as well. I understand this is from the dev branch and you are likely actively working on changes.
Back to my S905X for now.