1. adb reboot bootloader
2. fastboot --disable-verity --disable-verification flash vbmeta vbmeta.img (take the vbmeta.img file from your current firmware)
3. fastboot reboot fastboot (because gsi must be flashed in fastboot
d )
4. fastboot getvar is-userspace
5. fastboot erase system
6. fastboot delete-logical-partition product_a
7. fastboot flash system YOUR_GSI_ROM.img (system.img)
8. fastboot reboot recovery
9. (in recovery) wipe data
10. (in recovery) reboot to system
i flashed yesterday Arrow OS lite A12 it has several fixes for most common problems on board and it worked very well and smooth.
on telegram you can found a magiskmodul fix for auto-variable Hz and a magisk modul for disable hw-overlays consistent. (cauz after reboot it turn back on automaticly)
BUT gaming performance is horrible and good kernel tweaks are over my level