Nintendo Switch cartridge based games have a file that’s unique to each individual cartridge. The dumper and accompanying flash cart make use of that file. If Nintendo detects two people playing while connected to the internet with the “same” cartridge, there’s a high chance of them banning both consoles. So any used game anyone buys after this point runs the risk that someone dumped it, maybe an old owner who resold, maybe someone who bought and returned it, etc, which means even a legitimate user who hasn’t even heard of the flash cart could get banned. There’s also the potential issue of people using the tech in the flash cart once people figure out how to use those chips to sell bootlegged reproduction cartridges that have the same issue
Was technically possible to dump the unique cert with a modded Switch prior to this so even used games bought before could technically be impacted, but there was no real reason to do so since modded Switches and emulators would work just fine without it. Since it’s required to use the flash cart this dumper is a companion to the risk goes up dramatically