How to schedule airplane mode?
This is possible in iOS 14 using the Shortcuts app. You have to create an automation to enable the airplane mode in the evening and another automation to disable it in the morning.
I used the following:

Create automation
At 22:30 → Airplane mode ON
Disable “Ask before running”
Finish

The same process for the morning

Create automation
At 5:30 → Airplane mode OFF
Disable “Ask before running”
Finish

Another approach.
On the other side, since many would want to schedule the Airplane during the night, I can recommend from my own experience that leaving the  devices (phone, computer, tablet), in a different room than the bedroom is a good idea.
I built this habit in the last months and I use my CASIO watch to wake me up every morning.