This will probably be a pain, but before JetPack 5 (L4T R34+) an Ubuntu 18.04 host PC was required. I won’t guarantee it, but when you are using an older release (despite using a newer GUI frontend), I suspect you will need to use an Ubuntu 18.04 host PC.
I also won’t guarantee this, but in the past some people “faked” using a different Ubuntu release. See:
https://forums.developer.nvidia.com/t/sdkmanager-not-supported-on-linux/71742/4
(you’d want to make it look like 18.04)