I don’t have a passcode reset button for the screen time passcode

These are the minimum requirements to reset the ScreenTime passcode:

• The device must run iOS/iPadOS 13.4 or later;
• You must know the Apple ID & Password that were used to set up that ScreenTime Passcode;
• If you are part (member) of Family Sharing, ask the Organizer.

If you meet ALL above requirements, these are the instructions:--> If you forgot your Screen Time passcode – Apple Support

Shouldn't be this case, you need to erase that device following these instructions (even if related to the passcode to lock/unlock device's screen):--> If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

The bad news is that you cannot restore data from a backup, since the ScreenTime passcode would come back in.

Regards

Giulio

Yes, a model 6 cannot support iOS versions past 12.5.7, because of hardware (CPU/RAM) limits.

Unfortunately, you have just the 2nd option.

Regards

Giulio