So, playing the the Pokemon Sword and Shield Crown Tundra DLC, and I saw an article claiming you can break the game with it. Basically, as soon as possible you go to the Crown Tundra (which you can do as soon as you finish the opening ceremony of Galar's League and fight your rival Hop). There's an obligatory trainer battle against a man with lvl 70 Pokemon, but you don't have to beat him. So as soon as you lose to him, you go to the DLC's big "gimmick", which is the Dynamax Adventure dungeon, where you move from Dynamax raid battle to Dynamax raid battle until you reach the Legendary at the end.
The thing about this is that you don't need your own Pokemon for this, since the dungeon gives you a properly-leveled rental Pokemon before going in. You then go through the battles, catching the Pokemon if you want, until you reach the Legendary at the end. Even if you don't reach the legendary, so long as you caught at least one of the Dynamax pokemon, you get to keep it (though you only get to keep one of the Pokemon you catch). Doing this leaves you with a lvl 65 Pokemon in your party before even reaching the first Gym.
I tried this (creating a second profile like the person claiming this game breaker did) and tried it. And... Yep. It works. The game on my second profile currently has me with a lvl 65 Dusclops, and I haven't even gone near Turffield or its stadium.