I went for this method of replacing the SSD. It's less stressful than trying not to break the screen.

Ente is also self hostable. https://help.ente.io/self-hosting/

Are you checking between the 12V and one of these legs? It's typically connected to ground in these types of controllers. Here's the SOT23 pinoutfor reference if that is the same package.

I went over the FAQs and it looks like it measure current and know how much energy has passed through but I wonder how it handles if you plug in the device at a different initial charge.

That won't work either, it needs a Bluetooth connection to know the phone's charge which means the phone needs to be on.

It will only reboot once unless it is unlocked again https://grapheneos.org/features#auto-reboot

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.