The case for Iphone XS is the same as the one from Iphone X

It will fit but the iPhone X's speakers on the bottom are slightly different, so you will be covering them up if you used an iPhone XS case. I personally wouldn't use an iPhone XS case for that reason alone.

According to various third-party Apple news sites, the 'bump' of the dual-lens camera is a millimeter taller/wider than its predecessor. e.g. Larger camera bump in iPhone XS may prevent reuse of some iPhone X cases

The answer, sadly, is no. It's not the fit you'd expect from the case that is designed for the device. If you want to replace your leather Apple-branded snap-on case for a X, you can't. I spent a good deal of time yesterday texting with Apple support and talking on the phone with them to try to find a replacement for my leather, snap-on Apple-branded case, which is pretty worn after a year of daily use. No one could help. The last advice I got was to go to my local Apple retail store and check with them. I did, and I was given the implausible explanation that that particular case was an "anniversary model" that was only available for the iPhone X to commemorate the 10th anniversary of the iPhone. The Apple store employee was unable to finish the story without a telling smile. I find it astonishing that I can get a leather Apple-branded snap-on case for my daughter's iPhone 8, but not my own X.

Yes.

Maybe.

https://www.macrumors.com/2018/09/19/iphone-x-cases-may-not-perfectly-fit-iphone -xs/

A bit of careful cutting or filing of the case's camera cutout may fix it.

Yes but there is a slightly different around the camera. I have tried in the apple store. I think that does not affect a lot but for me I can not accept that.