If there are no marks on the screen itself, the problem is likely the screen protector - especially since it's a generic brand.
If you Google "iPhone 12 teardown" you'll see there is nothing circular in the screen that would cause this. Underneath that is the rectangular battery that's takes up most of the phone.
In fact, the only thing circular in the 12 is the magsafe charging port - but that's higher up, larger, and centered horizontally relative to those marks. It's also in the back of the phone, not the front.
What makes more sense is the protector is defective because of too much vacuum pressure applied during manufacturing, so the sticky surface is not consistent and the marks are only visible after applying to the phone. Between everyone in the house, we've gone through hundreds of protectors over several generations of iPad, iPhone, Galaxy, Surface, etc. and it's not unusual for generic ones to lift at the edges, form marks like this, and plastic being marketed as glass (folds and scratches easily).
I'd estimate about 20% of the ones we've used come close to the quality of a reputable (but much pricier) Zagg InvisibleShield or Belkin UltraGlass. Over time, we've realized if we're already spending $800+ on the gear, it makes sense to spend the extra 20 to give it good protection. For comparison, the "real ones" are thicker, have a smoother texture, and lasts a lot more drops.
So, I suggest trying a different brand to see if that makes a difference. If you can afford it, a good brand practically guarantees an answer to whether it's the phone or the protector.
