It's weird that Airplane Mode is the only solution found on the forum. Sometimes the purpose is to completely isolate the phone from any cellular networks, once and forever. You don't want to find out that you accidentally toggled it off and started communicating with the towers again.
de0u That sounds very likely. But GrapheneOS, unlike other Android variants, stays up to date with AOSP updates as frequently as weekly. This means that every feature added by the GrapheneOS developers may need to be re-done and re-tested weekly. This is the most troublesome when a change is made to a part of the system that Google changes frequently -- which includes the quick tiles.
As there is no secure way to use cellular networks whatsoever due to hardware identifiers that Graphene won't target soon, I can only think of turning the phone into a simple Wi-Fi computer with no other connections at all as a reasonably secure way to use Graphene. Why taking the risk of turning the Airplane mode back on? What if it happens and you forget about it for a while? Even without ever inserting a SIM, looks like leaving a trace of a Pixel IMEI along the way may carry a risk. Maybe it's possible to add a setting that does not allow the phone to function unless cellular is off? Or specialized builds that strip the OS off the cellular module?
Haven't used Graphene yet, I hope it's not possible to turn Airplane mode off without unlocking the phone, right? Maybe it's possible to require additional authentication before toggling it off? And is Airplane Mode even hermetic on reboots? Or could the device briefly communicate with cellular networks before the software fully loads the settings?
As sometimes there isn't any intention to use cellular networks at all, a hard toggle would be a nice thing to have, so even if you have non-root access to the unlocked phone, it should be much harder to get it back to work. Preferably stripped off on build level though, for those who're not willing to risk at all.
And yes, you can say "just use an Android VM" if no cellular usage is intended, but for a daily driver it may be overkill. With a rooted phone you can stop the cellular module completely, so you'd expect a built-in solution from Graphene that does not require rooting.