What I did, quickly summarized and if I recall correctly (no guarantee):

1. Enable developper mode and allow the USB debugging (Just as the first step of the easy installer)
2. Install adb and fastboot (and check it works)
3. Downloaded the latest version of the Android 12 branch for Pixel 5 from https://developers.google.com/android/images and unzipped it
4. Ran the "flash-all" script for my OS

You might want to check https://droidwin.com/restore-google-pixel-5-stock-firmware-fastboot-commands/