Your bootloader is rather old-ish. I would look into updating the bootloader on your RPi 400.
There was a recent case, not quite similar’ but a non-booting install nevertheless where updating the bootloader resolved the issue. (See here: [noob] cannot boot from base install on rasp pi 4 4gb)
Please do a bit of research of your own and make sure you understand the implications of modifying your device in any way. The responsibility is all yours
