I have the same issue. It's surprising there is not a straight forward resource on how to use PassKit. it's even worse if you want to use NFC functionality. Right now, I am just trying to get something into the Wallet app at all. It took forever just to get the certificate signing errors to go away. I've used the reference you listed and also this: https://developer.apple.com/library/archive/documentation/UserExperience/Conceptual/PassKit_PG/YourFirst.html#//apple_ref/doc/uid/TP40012195-CH2-SW1

It is absolutely unreal that this is still an unresolved issue. People WANT this ability. Those who do not want it also would not install a 3rd party screen time app on their device in the first place. This is not even an afternoon's worth of work that's been waiting years to be done.