I'd like to be able to just do...

    type UserType = 'default' | 'admin' | 'manager';

    interface UserTypeCounts {
        [key: UserType]: number
    }

Not the best example, but it gets the point across. When you do this it says the key must be a string type which it actually is. It's just a string limited to specific values.

Yes, I could do an interface with explicitly named keys instead, but if that type (or enum) could have dozens of possible values it's annoying to duplicate it.