For example, Steven has a Skarmory, so that would cover both flying AND steel. Are there any regions that have all the types in the gyms and E4? Thanks so much!
Most regions' gyms, Elite 4, and champion use every type, so I'll list only the ones that don't.
Kanto (RB): missing bug
Hoenn (RSORAS): missing poison
Hoenn (E): missing bug
Kalos: missing ground and dark
Alola (SM): missing psychic
Galar (Sw): missing electric and ice
Galar (Sh): missing electric