Yeah, I want to make a dedicated thread, but that's going to be for another day.
Anyway, it's pretty easy.
You'll need a modern fastboot (i.e. which supports Android 10's dynamic partitions), and we'll unlock bootloader.
Download vbmeta from
https://dl.google.com/developers/android/qt/images/gsi/vbmeta.img
Download an ARM64 A/B GSI, for instance:
https://github.com/phhusson/treble_...nload/v220/system-quack-arm64-ab-floss.img.xz
(
https://github.com/phhusson/treble_...nload/v220/system-quack-arm64-ab-gapps.img.xz if you want gapps)
- Enable developers settings, tick oem unlock, reboot to bootloader with `adb reboot bootloader`
- Do `fastboot flashing unlock`
- Accept the unlock
- As soon as you get adb back, do `adb reboot fastboot` (/!\ THIS IS NOT `adb reboot bootloader` it is different /!\)
- `fastboot flash system system-quack-arm64-ab-floss.img`
- Select "Reboot to bootloader" on the phone
- `fastboot flash vbmeta vbmeta.img`
- Select "reboot to recovery mode" on the phone
- Wipe userdata partition from recovery
- Reboot
At the moment, fingerprint sensor doesn't work on GSI (it shouldn't take me long though), so there is no point in relocking, I guess I'll make a guide when I have it working.