How to recover/reset the restriction code in screen time?

Restoring one phone will not affect the other provided you have somewhere to receive 2FA verification codes.

Having a screen time passcode set will not stop you opening the SE to receive verification codes for restoring the 12 pro max.

Are you sure you mean Screen Time Passcode and not the Phone Passcode?

If the 12ProMax is set up and running you should be able to get codes on that phone too.

Can you sign into https://appleid.apple.com ? even on a computer. If you can, then you should be able to add an alternative number for 2FA codes and a recovery email such that you can restore the either without problems. You do need at least one phone accessible and set up to get the codes required to sign into the appleid site.

If it is too complex (it is not easy) then make an appointment and take both devices to an Apple Store, or call Apple Support as you can get into a mess very quickly.

Apple Support

and/or

Genius Bar Reservation and Apple Support Options - Apple

Welcome to the Apple Support Communities.

See: If you forgot your Screen Time passcode - Apple Support.

Jack

Two ways

1 If you used your Apple ID when setting it:-

Open the Settings app on your iPhone

Select “Screen Time”

Choose “Change Screen Time Passcode” process

When it is available select “Forgot Passcode?”

Enter your Apple ID credentials

Choose a new Screen Time passcode

Re-enter the new Screen Time passcode to verify it

2 If you didnt use your Apple ID when setting the passcode you are in trouble.

You will have to move all your data and media to somewhere outside the phone, iCloud Photos and cloud storage or a computer are the usual options.

Completely wipe the phone to factory settings,

Then start again as a new device.

Bring back your data and media from wherever you temporarily placed it. You will lose a lot of your other data like chat histories.

You're welcome, good luck.