There are 2 other ways Screen Time limits can be ignored.
- If allowed, they can delete an app and then redownload from the App Store to reset the limit. The solution is to not all App downloads or deletions. Go to Content & Privacy Restrictions > iTunes & App Store Purchases. Don't allow "Installing Apps" or "Deleting Apps".
- If allowed, then can change the time zone to give them more time. The solution is to first go to Settings > General > Data & Time and make sure it is set to "Set Automatically", then go back into Screen Time and Contents & Privacy Restrictions > Location Services > System Services and make sure "Setting Time Zone" is toggled off. Now tap the Back button and go to the top of the "Locations Services" page and choose "Don't Allow Changes"
Another thing kids are doing is getting your Screen Time Passcode by setting the screen to start recording, then having you put in your PassCode. If you see a flashing red icon in the upper left, then the screen is being recorded. Of course this can be disable in Screen Time too by going to Content & Privacy Restrictions > Content Restrictions and shut off "Screen Recording".
There is also the case of kids resetting their devices to Factory Settings. Currently the best solution to this is to change their Apple ID password and not give it to them. With Find My turned on they would have to enter the password when reset and you would know what they did.
This will not solve all Screen Time problems and there is still more work that needs done.