That functionality used to exist on Android, but I haven't seen it show up on the past two phones I owned. Does it still exist in stock and xiaomi just got rid of it for whatever reason?
It definitely still exists on AOSP, and most vendors still have it. Xiaomi did get rid of it. It used to be available, then only available if you "disable MIUI optimizations", then it's been entirely removed. Whether this is to force you to buy two phones, or simply as a result of how amateurish the software stack on Xiaomi phones is up to debate.