I don’t use a case, just a screen protector. Been through a lot of screen protectors but the phone has taken a pretty solid beating and still functions like new with exception of battery life. Not sure a case is necessary unless Xiaomi make unusually resilliant phones which I think is unlikely.
I guess if you have a closed shell case it’d be fine for the screen, but in my experience the screen is the only part likely to break and I’d rather not carry the extra size and weight of a case