I have a somewhat similar problem with Smash ultimate. But for your problem, there are a few updates for ACNH. I would suggest installing each one of them 1 by 1.
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okay i might actually have the solution. Download tinfoil on your switch and download the latest update for ACNH there with...
So I am on firmware 9.2.0 (also had this problem on 9.1.0) I have accidentally deleted my SSBU data and saves. I am trying to update it straight back to it's current latest version (7.0.0) via nsp because i am banned. But every time I install it and launch the game it gives me an error saying "...
yo guys the sonic x shadow generations trailer dropped today, and shadow just straight up decided, and i hate (love) to bring this dead meme up, but, it's morbin time