I can’t promise anything for sure, but the Radxa Rock 5C seems very similar to the 5B (except for the form factor). So maybe you might be able to use the same procedure that I used with my computer.
https://forums.opensuse.org/t/tumbleweed-on-radxa-rock-5b/
The Agama installer lets you choose between Leap (version 16.0 right now) or Tumbleweed (rolling release). Once you’ve chosen your distribution then you are able to choose KDE as your desktop environment (just as I chose Gnome as mine).
I hope that helps a bit.