I'm on the exact same journey as OP but I think I have a solution that is a little easier to setup.

Simply use Apple's Screen Time but lock all of the Screen Time settings behind a pin. Have a friend or loved one create the pin and keep it secret from you and voila.

With Screen time you can have an "Always Allowed" list and if you use the "Downtime" setting it doesn't actually let you set limits past a one minute exception per app.

You also have to make sure that the downtime setting is 24 hours of downtime.

*Edit: seems like a lot of people are suggesting the same exact thing.