This used to work great and is still my preferred method of back up, however for at least the past year it has been extremely unreliable. I have to manually load iTunes on my computer and initiate a back up from there because it never happens automatically anymore. And there’s no way to manually start the Wi-Fi backup from my iPhone anymore (that was removed in iOS 13). Maybe it’s more reliable if you use a Mac instead of a PC, but at this point I get a full backup maybe once a month, and often end up plugging in via USB cable in order to even get that.
(to clarify, my desktop PC is always turned on and connected to the network, so most of the other complaints in this thread about it not working with low battery laptops or whatever don’t apply in my scenario. Even in my ideal-case scenario it still barely works)
Worth mentioning iMazing by DigiDNA fixes a LOT of the issues around Apple's poor implementation of iOS <-> PC/Mac support. You can use it to schedule automatic wireless local backups, among other things.
(to clarify, my desktop PC is always turned on and connected to the network, so most of the other complaints in this thread about it not working with low battery laptops or whatever don’t apply in my scenario. Even in my ideal-case scenario it still barely works)