I'm have a nintendo developer account and found my unity plugin on an archive webpage, I don't know why it wont work for you at this point. You will need to activate it with that key if you want it to develop. Maybe deleting all traces of unity and reinstalling may make it ask for a key. But i'm not sure if it will work. I hope you can get it to work some day!Not asking me for any key, it Just logs in
btw, and this can be the problem, i have those archives downloaded from a while ago (2017) but i never opened them because i bought my Wii U recently and then i can't develop in it, but now i installed them to test my game, but maybe it's not atached to my account. So if that's the problem, thanks for help me to try to install it,