iPhone XS replacement display

Assuming you're talking about the ones for sale here on iFixit, since those are original Apple screens, they'll be soft OLED for both the used and new screens. You also have the option of getting a much cheaper LCD version.

Otherwise, the ones you can find on places like Amazon, eBay and AliExpress come in all three flavors; LCD, hard OLED and soft OLED. You do have to be a bit careful in ordering them, though, as they're not always up front about which one you're getting. Generally the cheapest ones are LCD, midrange prices are usually hard OLED and the most expensive ones are normally soft OLED.