Screen time Passcode

You will need to erase your device.

And you cannot restore from a backup after, because the screen time passcode is saved in the backup.

You have 2 options how to erase device:

Erase a device in Find My iPhone on iCloud.com - Apple Support

or following the same steps as if you forgot passcode:

If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

Good luck!

Follow these instructions—>If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support and do not restore a backup; set up the phone as New. (The screen time passcode is saved in the backup and would be restored with the backup).