The other user told me to do it this way (which I might swear I did back in the day without success, but can't be 100% sure):I tried and couldn't get USB host to work with my Fractal AM4 either. It just shows "not connected". Tried the toggling trick and it didn't seem to help, and the USB-C vs USB host port doesn't seem to make a difference either.
Both units powered off.
Connect the usb cable between them. Of course, the A port in the M1.
Power up both devices with power supplies (not relying on the M1 to power the Fractal). Wait until both have booted.
No matter what the USB setting is currently in the M1, go and select "device", and restart everything.
Now, select "host" in the M1 and restart.
Then it should connect (according to this mate testimonial).
I can't try this because I now have the prototype board in my M1, so to try it I'd need to dissemble it and assemble the old one... And It's something I don't want to touch now, honestly. I'm not very confident that this trick works... Because, as I said, I'd swear that I already tried when I had the original board.