SSD Ready Ubuntu Unity 20.10. Raspberry Pi 400, Pi 4.
Download from http://linux.darkpenguin.net/distros/ubuntu-unity/
I wrote the image to an ssd with Raspberry Pi imager. Worked on my Pi 4 8GB and Pi 400 4GB. Pi 4 needs an eeprom update that supports usb boot, you most probably already have it.
New Raspberry Pi imager Vs Balena etcher speed test
USB Boot the Simple way. Raspberry Pi OS. Pi 4.