Usually, when you hatch a Pokémon egg, you’re left with the earliest creature in an evolutionary line. This monster will only know basic moves. If you want a stronger creature, you have to level it up ... that is, unless you know of a new exploit discovered in Pokémon Sword and Shield.
The trick is simple, yet tricky — you need exact timing. First, you get the egg parent of the same species and place it in your party. The parent needs to be one rare candy away from leveling up and evolving. Then, you put the egg directly below the parent in the party menu. From there, you take the rare candy and use it on the parent. Immediately upon doing so, press down and hold the button. If you miss the timing, nothing will happen. But if you get it right, the process will somehow affect the egg, rather than the parent. The game will say that the egg is “evolving,” which shouldn’t be possible, except that it is! You can see it in action in this video by Austin John Plays:
You still need to actually hatch the egg, but once you do, it won’t be a baby — it will be evolved. You can use this process to skip the typical evolutionary process and go straight into, say, a monster’s final evolution. Except that “evolved” monster will be level one, somehow.
You can also use this exact same trick to teach an egg TMs before it actually hatches. The moves need to be in the Pokemon’s actual repertoire, but still, it’s a neat (and bizarre) trick. That’s not all: you can also use this method to bypass an evolution’s gender requirements, thereby allowing you to do things like hatch a Salazzle from a male Salandit (which normally wouldn’t be possible.) Wild, but also, proceed with caution, as there’s no telling whether or not Game Freak will patch this out.