NUSspli was ridiculously slow for me but give it a shottry using NUSspli. it will download and install on the system itself iirc. I've never used it though, just know of it.
I give up and used parallels on my Mac (worked fine)
--------------------- MERGED ---------------------------
NUSspli was ridiculously slow for me but give it a shot
here's that app. I'm not on linux to verify what works or not from that perspective. https://gbatemp.net/threads/nusspli...nintendo-update-servers-to-your-wii-u.566055/
you can try with either FunKiiU (https://github.com/llakssz/FunKiiU) or JNUSTool (https://github.com/Maschell/JNUSTool), both dont need windows