How exactly does WiFI password backup work?

A

AC Question

As of lately, whenever I flash a new ROM or install a new vanilla version of android on my devices, I do the opt in for the google backup hoping that information about my settings (doze, do not disturb, wifi passwords, etc) get backed up so I dont start from scratch everytime.
Despite of this, everytime I set up a new clean install, I find out all my commonly visited places I have to re-enter my wifi password (parents house, frequeted coffee shops, etc). Arent these supposed to be backed up with the google opt-in thingy?
I even do the NFC thing where you touch your device and it passes the info one to another (eg, from my phone to tablet) and nothing.
I also use Titanium Backup but cant seem to find the specific function for this. Do I just overwrite the settings app? Im sort of new to ROMing and stuff and Im afraid it will mess up my devices...
Please help!