Pokemon Scarlet And Violet Catch All The Flak For Poor Performance And Visual Bugs
We do have to take the refund reports with a grain of salt, as they're simply Reddit posts, and no one has posted a screenshot of any kind of proof. Still, there are several users in the thread reporting that they were refunded. This is notable because Nintendo doesn't normally offer refunds on digital purchases, although it's possible that some users might be getting refunds through retailers like GameStop or Amazon.
Some of the other issues are more serious, though. You can lose minutes per hour of playtime to weird performance problems and unusually-slow load times, and users have also reported lost progress due to game crashes. It's very difficult to maintain immersion in a game when the background elements and NPCs are glitching out and not rendering properly.
To be fair, some users are reporting minimal issues, and it's been theorized that perhaps the problems are localized to older Switch consoles, or players who haven't restarted their Switch systems recently. For what it's worth, many of these same issues crop up even when playing on emulators. With that in mind, they do seem to be endemic to the game, but maybe some folks are just lucky.

There are issues with the games beyond just bugs, though. Many fan-favorite features from previous games have failed to return in Scarlet and Violet, like Mega-Evolutions. Even little things, like a specific sound cue when a rare "shiny" Pokémon is nearby (added in Pokémon Legends: Arceus) are missing. Of course, like Sword and Shield, this game doesn't include the full national Pokédex, either.
If you're unhappy with your Pokémon purchase and you'd like to get a refund, the original poster on Reddit (/u/sellouthipster) suggests using his successful message as a copy-and-paste form letter. You can see that message in his post over here.