How to delete photos from an old iPhone without deleting them on a new iPhone?

I had just bought a new iPhone XS and now I want to delete pics from the old one but I don't want to delete the ones that were transferred on the new phone. When I bought the iPhone XS, the pics automatically transferred from old to new phone. Now I want to delete the pics that were on the old Phone without affecting the pics that are in the new iPhone XS.

Settings - Photos - turn off iCloud photos (you don't see the green tab).

That should stop the phones from sharing pictures. So if you take a picture on your new phone, the pic won't show up on the old phone and vice versa. If you delete a phone on one, the other won't be affected.

Take a picture that you don't care about, when it shows up on both phones, then do the settings-photos- turn off iCloud, delete the picture on one of your phone and see if it also disappears on the other phone.

Deleting from the old wouldn't delete on the new.