There is as well an experimental bare-metal target for raspberry pi 4 called gilbraltar https://github.com/dinosaure/gilbraltar. A big obstacle there is the device drivers. It is very cool to run bare metal on an rpi4, but it would be cool to be able use the network interface too.

EDIT: here as well: https://mirage.io/docs/install maybe you need a Solo5 backend that can run on ARM; and finally: https://github.com/Solo5/solo5/blob/v0.6.3/docs/building.md#...