First, is it the 2x camera or the ultra-wide camera that you are having issues with? They are on completely opposite ends of the spectrum. The ultra-wide camera is the 0.5x camera.
Second, you keep talking about the poor results from the ultra-wide camera and how you used to get so much better results on your iPhone 7. Your iPhone 7 did not have an ultra-wide camera. So why do you think comparing photos taken by this brand new ultra-wide camera that does not have the capabilities of the camera on your iPhone 7 is valid? The camera on your iPhone 7 is a better camera than the ultra-wide camera on your iPhone 11. The camera on your iPhone 7 IS NOT a better camera than the wide angle camera on your iPhone 11.
Third, yes that is lens flare in your photo of the Pisa tower. This is not the fault of the camera. If you had simply moved a little or turned the camera so that the giant bright light was not in the frame, you would probably have been able to remove the flare.
I actually saw an example of this today so I snapped both photos so that I could share them in this thread. These two photos are taken of the exact same area. I just moved slightly to remove the flare. Just to be clear, I am not sharing these as a demonstration of awesome photos. I actually snapped these just to use for this example because I thought it would be instructive to show that the appearance of lens flare can be mitigated by how we frame our subjects.