A little backstory:

I have an iphone 12 Pro on iOS 15 beta 8 as well as an inactive sim card so this will work with current model iphones and current iOS versions.

What I did:

This is a modified version of method 1/6 essentially so you will need an inactive sim card. Put your inactive sim card into the iphone and make sure the phone number matches with your phone number just as in method 1.

Next pop back in your active sim into your iphone and make sure imessage is working and you can send and receive. power down your iphone AND WAIT 2 MINUTES. Do not do anything until at least 2 minutes goes by.

Once two minutes goes by pop out your active sim and place it to the side for now. Take your inactive sim and put it into your iphone and DO NOT TURN IT ON, LEAVE IT OFF. What I think is happening is its tricking apple servers into believing your iphone is off with an active sim inside.

Finally place your active sim into your android phone and use it as normal. Go into preferences on you Mac and make sure your phone number is being used. As long as your iphone stays off this should work, ive been using this for 5 hours now and its been working so fingers crossed it stays working.

As with any method this is not guaranteed to keep working to do this at your own risk and keep in mind results may vary from user to user. Enjoy!