Below is a list of all types showing the non-legendary Pokémon of that type with the highest BST, excluding Pokémon not available in either Sword, Shield, the Crowned Tundra, or the Isle of Armor, as well as mega evolutions, since you can't get them in that game either:
Note: this answer assumes Mythical and Sub-Legendary Pokémon count as Legendary Pokémon, but Ultra Beasts do not.
Bug: Tied between Pheromosa and Buzzwole at 570
Dark: Tied Between Hydreigon and Tyranitar at 600
Dragon: Tied between Dragapult, Kommo-o, Goodra, Hydriegon, Garchomp, Salamence, and Dragonite at 600.
Electric: Xurkitree at 570
Fairy: Togekiss at 545
Fighting: Kommo-o at 600
Fire Blacephalon at 570
Flying: Tied between Salamence and Dragonite at 600
Ghost: Dragapult at 600
Grass: Kartana at 570
Ground: Garchomp at 600
Ice: Galarian Darmanitan (Zen Mode) at 540
Normal: Tied between Snorlax and Blissey at 540
Poison: Nihilego at 570
Psychic: Metagross at 600
Rock: Tyranitar at 600
Steel: Tied between Metagross at 600
Water: Wishiwashi-School form at 620
Source: Pokédex with stats--Pokemon Database
Hope I helped!