You can put them in groups using an ACF select type field.
The real question is what are you going to use the field for. No matter what way you turn you’ll need to either do something like adding the roles mentioned or doing a custom query on users with a meta_query on the field to get users in a specific group.
And if you’re talking about limiting access to certain pages based on this value, then in either case it’s going to require custom coding.
