Tried that, still prompts, maybe I done it wrong or it doesn't work for game updates.
I tried an original cart that I've never even used yet (Arms) and that was claiming software update available as well. It's not a system update prompt as it's on the latest 5.1.0, just thinks games have an update for some reason.
I didn't think of this before and I've hardly used my switch, so not sure how it works. But when I went online to get 5.1.0, Mario odyssey was in the recently played games list as it was what I was playing before I got my sx pro. That definitely has an update and the console had never been online before, so previously wouldn't know about it. Is that the problem? Is it just a general flag, the system knows a piece of software (Mario) has an update, so now just harrases me no matter what software I launch to get the system back online to get the update?