Dragon type.

One of the most op types in the game it got nerfed when fairy type was introduced but it still is very powerful.

My gym leader team

Duraludon: to cope with the fairy weakness

Dragapult

Hydreigon

Kommo o

Tyranitar

Garchomp

Bug type

Steel, I dont think that there has every been a steel gym as of now

Team: Lucario, Bisharp, Bronzong

Jasmine and byron: am i a joke to you?

Steel- my team would be Copperajah, Corviknight, Lucario, ferrothorn and Dialga

Dark. With a team of Houndoom, Hydreigon, Honchcrow, Weavile, Zoroark and Krookodile. If three then Houndoom, Hydreigon and Honchcrow

Fairy.

I'd at least have a Grimmsnarl. I'm blanking, but Fairy is my favorite type.

Flying.

I'm working on a fanregion in which the Flying gym leader is basically me. Her team consists of a Corviknight, a Honchkrow, a (fanmega!) Talonflame, and three Fakemon.

Poison or electric.

Poison: gmax toxtricity, skuntank, seviper, scolipede, gengar, toxicroak

Electric: Luxray, Zebstrika, dracozolt, gmax toxtricity, galvantula, mega manectric.

Steel.

My team would be Solgaleo, Duskmane Solgaleo, And Galarian Meowth