fwiw, installing GrapheneOS is by far the easiest phone OS install I've ever done. It's been a while but if there were any hiccups, they were too small to remember. My memory is just plug it into desktop with usb-c cable, go to grapheneos website in chromium (it uses web usb so no firefox), hit the install button, and wait a couple minutes.

And yes, it allows you to disable network permissions for apps, among many other nice things.