Honestly they kinda screwed over people -- like me -- who tried to avoid the MAX planes for a while. I'd specifically book around the MAX planes and then they would change equipment at the last minute into a MAX. There is no meaningful "knob" an aviation consumer can turn to express an aircraft preference, and given how US airspace works, you often don't have a meaningful choice in carrier (unless you're willing to take on extra stops).
In the US (parent mentioned US specifically) I think that's just Frontier now that Spirit is gone. I mean technically that's doable sure but idk if I would say trivial it's really limited on routes and the experience is terrible from what I understand.
