Update: This is still happening and I'm on iOS 15.1. One caveat to this is that it appears to only be happening on foregrounded apps. The home screen does not have this behavior, as I'm able to interact from the left side of the screen. It's possible that Apple has done something to the swipe navigation gesture recognizer on the left side which lets you swipe to go back in a push navigation hierarchy, but I think I've also seen this in apps that don't appear to be using a navigation controller. This is definitely an iOS 15 issue no matter what anyone else tries to tell you.

Yeah, I have this issue there, too. Do you see it happening on your home screen? I take back what I wrote above about it just being the left side of the screen not working; also seeing a chunk of the middle vertical portion of the screen not working, in addition to the touchscreen being very unresponsive, erratic, and jumpy in general (pinch-to-zoom, app carousel, swiping to get to the home screen, etc.). In addition, rotating the screen into landscape makes the glitch go (because of the rotation) across the whole bottom of the screen (space bar of keyboard and anything else at that level doesn't work) but for some reason the middle screen glitch seems to go away then. Sometimes I can get the "a" key to work but nothing to the left of that on an English keyboard ("q", shift button, etc.) ever works for me!

Nope, still doing this on iOS 15.2. Took my XS in to an Apple Store today, they did a hardware diagnostic and screen is coming up fine. To rule out software issues, they said to wipe it and see if the behavior persists when you go through the process of setting up the phone again—still doing this for me. They said to bring it back in again if it's still doing it, so I have another appointment tomorrow with them. Will update.

Did this behavior start when you upgraded from iOS 14 to 15?

Well, there's the iPhone X display module replacement program: https://support.apple.com/en-au/iphone-x-display-module-replacement-program. They need one for the XS!

They ran a hardware test and identified the same issues as I've been having by drawing on the screen. They said it's a hardware issue and not a software issue, and when I said it was working perfectly fine under iOS 14 they said sometimes updates can exacerbate underlying issues. I should've asked them how they could know it was a hardware issue and not a software one. The phone is out of warranty so I'd have to fix it out of pocket (which isn't cheap). Just for my own peace of mind, I may try downgrading to iOS 14 and see if it works then (I've looked up how it can be done, doesn't seem easy).

Yeah, it's not a good answer. They're basically trying to say the issue was always there or something. And your issues started when you upgraded from iOS 14 to 15? Depending on the country you live in, you may have different consumer rights and protections for a screen replacement. I live in Australia where they seem to have pretty strong consumer protections, so I'm trying to pursue a fix under them. As far as downgrading to iOS 14 goes, it's not easy! If you search for something like "how to downgrade ios 15 to 14 unsigned" you'll see a few guides. There have been two sets of screen module recalls for the iPhone X and the iPhone 11 and I asked at the Apple Store what it would take for there to be one for the iPhone XS. The tech I was talking to said it probably would've happened very shortly after the phone's release as hardware issues became identified, and that it was unlikely a recall would be initiated 3 years after the device had been out.

I upgraded to it last night; still happening.

I was about to say that the issue didn't seem widespread enough to get Apple to pay attention (based on me looking this issue up a while ago and not seeing much about it), but I just looked this issue up again and found a lot more, especially an OSXDaily article which of course I can't link to on here. It has links to a bunch of different comments with users across a range of devices having issues with iOS 15. Have you gone to an Apple Store? What are they saying? I'm pursuing this a different way because I live in Australia and we have pretty strong consumer laws. I bought my phone refurbished and am trying to go after the company I purchased it from. Since Apple are saying it's a hardware issue the screen shouldn't be failing this soon. This may not be an option in Europe (since you said "euro") but maybe you could have a look and see fi there's anything applicable in the EU around this?

Does there need to be an Apple Store in your city? Can you contact Apple elsewhere in Germany or the EU about this? I was able to get the company I bought my phone from (it was refurbished) to agree to take it back and replace it. I'd contacted a government consumer advocate division in the state I live in and they advised me how to approach the company. Is there a similar group you could contact in Germany or the EU? Australian consumer law states that an item you've purchased from a company (even if second-hand or refurbished) has to be fit for use and there are no time limits on it (it's a reasonable expectation of how long it should last based on how much you paid for it and what went wrong). It's over and above any other warranty. Not sure if there's something like this in Germany or the EU but you could research it. I'm not sure if Apple would "fix" this as they seem to be saying it's a hardware issue, even though that hasn't been our experience.