They can be dual-typed, but at least one of those has to match the type you choose. What type are you choosing, and what’s your team look like?
I would have to choose Bug-type, of course. Team composition would be Galvantula, Yanmega, Heracross, Centiskorch, Genesect, and Rabsca. As to why… I just like 'em, lol. I’m not much of a competitive player. What would your team/type be?
I would go with fairy types. My team would be Sylveon, Tinkaton, Gardevoir, Galarian Rapidash and Flutter Mane.
My reason for the team is that I really like the design of them and I just like them overall. They can also receive and deal a huge amounts of damage. Sylveon have almost exclusively managed to carry me through the games.