When trying to rung Ubunto Server on a Raspberry 4 with 4 GB RAM, you might end up with the same problem as me: USB is not working at all.
The cause is a kernel bug affecting 4 GB version of the Raspberry 4 Model B only. 1 and 2 GB versions are working quite fine.
The issue has been identified and it’s been found to be a kernel bug with a solution in the works that being tested. In the meantime, you can access to your Raspberry Pi 4 4GB USB ports by limiting the memory to 3GB in /boot/firmware/usercfg.txt […]
To limit the available RAM to 3 GB just add
total_mem=3072to the usercfg.txt.