I presume the Linux version is the same (I used the Windows version) but WiiUDownloader gives you a lovely graphical interface to download anything from the WiiU eShop servers. Even copies files straight to an SD card ready to install on your WiiU.
I haven't bothered with any sort of NUS downloader in years because converting the content has always been a pain in the ass. In the past couple years there's been multiple WiiU rom collections uploaded to archive.org . Just recently, I set up my WiiU with a 4TB hard drive and used JDownloader to pull the entire North American WiiU library in USB installer format over the course of a couple days. Installing everything was a bit of a chore, but at least I didn't need to deal with any conversion on the PC side.
i know this isnt super helpful but i used a tool on my steam deck that could both download and decrypt wii u games through a gui, i dont remember the name though. it took a while for me to find while i was looking for alternatives while trying to get other tools to work