I can understand that!
Returning to stock is done through fastboot so you just need to get the phone in fastboot mode at the beginning of the process. You can do this button press combo: with device powered off, hold vol down and press power to start the phone . Or with cable in phone hold vol down and plug other end into pc. Same thing.
I’ll just get some more info…
download the last android 11 for sunfish from here
https://developers.google.com/android/images#sunfish
The instructions for flashing are at the top of the download page but I can help if you need it.
Here is a log of the last time I flashed 11 on a pixel 5 this way, so you know what to expect as output in the terminal. Ah I can’t seem to post it I’ll try again in a bit!
Hmm, the forum will not process .txt file and I don’t want to paste the entire contents here; there’s about 140 lines of text.