iPhone 13 is rumored to have a thinner notch but the phone itself will be thicker according to John Prosser. iPhone 13 notch has been predicted to be thinner for a more modern design. The actual phone itself will be thicker by 0.26mm.
John also talks about iPhone SE 3 will not be coming as there are no reports about it. But the iPhone 13 notch might be getting smaller with no big hardware changes to the camera.