iphone xs intermittent touch

My iphone XS, just over two years old, has started having frequent problems with intermittently not recognizing touches. I also have occasional ghost touch problems, but the main problem is that it often won't recognize touches. For example, for a while it wouldn't recognize the letter y when the phone was held vertically. Now y is fine, but the letter a doesn't work, nor does the back arrow at the top left corner, as used in various apps. I can sometimes work around this, in apps that let me rotate the screen and get a horizontal keyboard; then the "a" is fine. Occasionally other touches are not recognized as well. Even weirder is that sometimes it will be fine, and then sometimes it gets really bad. It happens across all apps, same locations on the screen.

I have tried updating to the latest iOS (14.3), updating all apps, cleaning the screen (often), using it without a case, restarting the phone, doing a hard reset. I'm leery of doing a full reset to the original factory config and reinstalling all my apps, configs, etc. manually. That's a ton of work, potentially for no benefit. All the behavior suggests to me a hardware failure. (Unfortunately, my warranty just expired.)

Any suggestions would be welcomed.