Ubuntu (a distribution) or Linux in general? Ubuntu tends not to be ported to that many things that are not PCs or some phones. Debian (what Ubuntu was originally based on) gets ported to basically everything that can take it along with a lot of its library (though it is still going to be non X86 hardware, X86 and X64 being PC for those following along at home, so you will be missing things and not able to run X86 code outside of whatever emulation layer you care to use).
Most wii homebrew can be made to work on the Wii U but probably not ideal/does leave a lot unused.
Native Wii U linux never quite got as active as Wii, Xbox and such like efforts where people actually quite liked doing it. To that end you are unlikely to find too up to date premade distributions and
https://gitlab.com/linux-wiiu/linux-wiiu is going to have to be your guide to doing what you need to do, though it is far nicer today than hearing "compile your own kernel" back in the 90s and early 2000s.