If you’re not upgrading, it’s probably easiest if he doesn’t, so you’re using the same version.
But as we said in our coverage of iOS 13.3:
As in the past, if you have already upgraded to iOS 13, we recommend installing these updates soon. The bug and security fixes are sufficiently important that you don’t want to wait long. Those who are still using iOS 12 should wait a bit to make sure Apple didn’t introduce new bugs with 13.3, but it’s probably safe to upgrade after that.
Well, I thought that too, but our phones are so different that there are definitely differences on how the OS works, even being on the exact same version!
I thought his said 13.4 was available but it looks like I was wrong, mine says 13.3
I’m still wrestling with what to do with mine but that’s a whole other topic.