I have one too and it’s been great. They sell replacement parts including the rubber liner if you need one soon: https://www.litter-robot.com/litter-robot-4-globe-liner.html

According to elegoo’s firmware instructions, the screen itself has updatable firmware too. Maybe you could try updating that as well

I found this diagram for V2.2 which looks the same. The lit LED is D5 which is the one you mentioned on the 3rd page. It looks like it only indicates that the 5V to 3.3V regulator beside it is working and has power.