If you are restoring from a backup that was on an older version of iOS to an iDevice running a NEWER version of iOS then it's no problem. It's only a problem if you are trying to go the other way. You can fudge it if both devices are on the same version, but different point releases. Say restoring a 15.6 backup to a device running 15.1.
That said, Apple has things down now. When you go to set up the new phone you won't even have to worry about that. You will be given the option during the new phone's setup to transfer all your data from the old phone to the new. iOS will walk you through that. That's how I transferred my daughter's old data from her 6+ to an SE 2020.