Cashiers checks can be shredded and the funds won’t be removed from your account, you shouldn’t have to deposit your own check into your own account. Actually, you shouldn’t be able to deposit the check because it can only be cashed by the person it’s made out to.

Either way, that’s not the issue here and it’s just confusing things. The issue is that you paid a deposit for a room, you returned the room in good condition (right???) and now you’re owed your deposit back.

Like I said before, next steps for you should be to take pictures of the room to show its in good condition, send the landlord an email asking for the deposit back and nothing else, and if they say “no” then demand they show you the reasons for keeping it.