Not sure if this is the correct category…
Running an older UBPort, there was a notification for an update.
That got stuck in a restart.
I could once enter recovery (power off the device and power up again with Volume up pressed to enter recovery) or fastboot and tried an update with Marius Device Tool: https://github.com/MariusQuabeck/magic-device-tool
That all started fine, however at the moment that the real work should have started, the phone couldn’t be detected.
Now the phone does nothing. All I see is a red light when attaching the loader. So it looks pretty dead.
Any idea what I can try?
The red light could mean that your battery is very low.
Leave your phone on a charger and see if you still can charge the battery.
The red light should turn in to yellow and when fully charged into green.
So the first part of what you describe is what happens with me too. Pushing the power button shows (small) loading ??/100%
Then after hours connected with the loader, still looks pretty dead.
Doing the same steps again (out for >hour, connecting, …) shows a yellow-white light for some time, that disappears. Pushing the power button still shows (small) loading ??/100%
So there is simply a battery/loading problem.