`fastboot flash boot <boot_image_name>.img`. I think
https://www.mobileread.com/forums/sh...d.php?t=336523 does a better job of explaining what to do in what order. You can get decrypted boot image by using
https://github.com/Hagb/decryptBooxUpdateUpx and then use magisk to patch it. The procedure is the same for most devices, the boot image is different, hence why you need to prepare your own.