I am running this on Ubuntu 22.04 LTS (64bit) both on a Radxa Rock 5b and a Raspberry Pi 4. I used Armbian to get Ubuntu on the Rock 5b, but I was able to install Ubuntu on the Raspberry Pi 4 using an image directly from Ubuntu's website (not Raspbian). I expect Ekos would work just fine on Ubuntu 22.04. The PPA certainly has 22.04 builds.
If I hadn't bought the Rock 5b, I would have bought the ODROID-M1. The ODROID-M1 sells with a nice, passively cooled case and also has NVMe storage. It's processor is just slower than the Rock 5b... but still on par with the Raspberry Pi 4.