Using Nov 2022 stats, before SV release:
Gen 8 Ubers:
- Bug: Pheromosa (5.45%)
- Dark: Yveltal (70.35%)
- Dragon: Eternatus (41.49%)
- Electric: Zekrom (10.89%)
- Fairy: Xerneas (38.32%)
- Fighting: Marshadow (27.78%)
- Fire: Ho-Oh (19.86%)
- Flying: Yveltal (70.35%)
- Ghost: Calyrex-Shadow (45.82%)
- Grass: Ferrothorn (8.02%)
- Ground: Groudon (19.47%)
- Ice: Darmanitan-Galar (10%)
- Normal: Ditto (6.27%)
- Poison: Eternatus (41.49%)
- Psychic: Necrozma-Dusk-Mane (53.8%)
- Rock: Tyranitar (5.01%)
- Steel: Necrozma-Dusk-Mane (53.8%)
- Water: Kyogre (30.95%)
Gen 8 OU:
- Bug: Volcarona (9.18%)
- Dark: Weavile (14.08%)
- Dragon: Dragapult (21.47%)
- Electric: Zapdos (10.12%)
- Fairy: Tapu Lele (14.78%)
- Fighting: Urshifu-Rapid-Strike (13.52%)
- Fire: Heatran (16.57%)
- Flying: Landorus-Therian (43.43%)
- Ghost: Dragapult (21.47%)
- Grass: Ferrothorn (20.4%)
- Ground: Landorus-Therian (43.43%)
- Ice: Weavile (14.08%)
- Normal: Porygon2 (2.93%)
- Poison: Toxapex (14.95%)
- Psychic: Tapu Lele (14.78%)
- Rock: Tyranitar (7.28%)
- Steel: Corviknight (20.73%)
- Water: Toxapex (14.95%)
Hope I helped!
Sources: Gen 8 Ubers 1630 usage stats and Gen 8 OU 1695 stats