For A/B slot devices (Pixel 6+ and newer), use fastboot flash boot_a boot.img and fastboot flash boot_b boot.img or fastboot flash boot --slot all boot.img .
Once you have your verified boot.img file, here’s how to flash it safely: Boot-img File Download For Android UPD
Xiaomi devices are popular among developers. For these, you need the Fastboot ROM (not the Recovery ROM). For A/B slot devices (Pixel 6+ and newer),