But I forgot something: the OS must first be configured to disable fingerprint / lockscreen, otherwise I won't be able to mount / install ROMs.
For some reason I fail to understand, when I rebooted into recovery, I could still mount internal storage, copy the official + gapps zip, and flash it. But after I formatted it and rebooted it... no more.
My guide is here:
Thanks for @urbanman2004 guide for Poco X3 Pro. Some sentences still needed, so keeping it similar. This guide provides photos & screenshots. Simulate all process and reduce misunderstanding. Section 1: Unlock bootloader (Works for most...
Follow Section 2.
If it fail for some reason, first format data, reboot to TWRP, put MIUI ROM zip in the phone, flash MIUI, format data, then reboot to TWRP again.
When any strange error encountered, it's recommended first go back to MIUI, then proceed flashing ROMs and other zips.
There are some bugs in the latest ArrowOS version 0723 of vayu. Download the 0709 version. Look in the reply of the ROM thread for that version.