can't change screen time passcode after failed attempts

On a Mac

1. Make sure that your Mac is updated to macOS Catalina 10.15.4 or later. 
2. Choose Apple menu  > System Preferences, then click Screen Time.
3. Select a child's name from the drop-down menu in the left sidebar. 
4. Click  Options in the lower-left corner. 
5. Click Change Passcode, then click Forgot Passcode. 
6. Enter the Apple ID and password* that you used to set up the Screen Time passcode.
7. Enter a new Screen Time passcode, then enter it again to confirm. 

If you have Share Across Devices turned on, your new Screen Time passcode will automatically update on those devices after you reset it. 

1. If you still have issues resetting your Screen Time passcode, contact Apple Support.

If you forgot your Screen Time passcode - Apple Support

Or...

Cannot reset Screen Time Passcode - Apple Community