To be fair, there are legitimate business uses for Mac. Video editing, for example. But I get your point. And I suppose a Macbook AIr wouldn't be what you get for that, anyway.
Delete the memory card file for that game, assuming you didn't change the default Nintendont setting which uses a separate virtual memcard for each game.
Ask the original seller if they have a clean NAND backup. Without it, you can't make the sysNAND 100% clean again. Factory reset does nothing. You can clear the logs with homebrew, but Nintendo can detect that the logs don't match what's on the...
btw i feel this a good time to remind you guys that sea of thieves was made by rare, who also made DKC1-3 and DK64, alongside banjo kazooie and conker's bad fur day