Used my iPhone X in the pool, now display wont work!

I'll start by saying that the iPhone X is water resistant and not water proof. These phones were never designed to be used under water.

In your case, it sounds like the backlight or backlight circuit was damaged. This could be screen related or logic board related. However, with water damage, you have to decontaminate the logic board before doing anything else, otherwise there will be latent issues down the road.

The rice myth kills too many phones! Let’s track this down together. This is a useful troubleshooter with common solutions for iPhones that are nonresponsive.

The water is inside the phone, on the logic board and under the shields, even under the IC's. The rice is nowhere near where the water is. So while it “may’’ soak up some water vapour, the real problem is the mineral deposits that can cause short circuits or the corrosion that is taking place as the water evaporates. Leaving the power on the device accelerates the process. The longer you let a phone sit in rice, the more time you are giving corrosion to damage your logic board. The saltier or harder the water is, the more damage will occur.

The iPhone X has a sandwiched logic board which makes it virtually impossible for a proper DIY decontamination but you can still try to follow most of these guidelines.

• Open your phone and remove the logic board (follow these guides)
• Inspect the logic board, especially around the connectors and look for corrosion.
• Inspect both sides of the board. Unfortunately, most of the board is covered in shields. That's usually where the damage is occurring.
• Put your board in a container with >90% isopropyl alcohol and let it sit for a while.
• Use a soft brush, like a toothbrush and lightly brush away any corrosion you see.
• Rinse in alcohol and repeat.
• Let it air dry for a day.
• Re-assemble and hope for the best.

A professional repair shop that does water damage repair may be able to recover your phone or the data because they have access to pro-level ultrasonic baths and specialized cleaners as well as the skills to troubleshoot your board. Many shops have a no fix/no fee policy so you don't have to spend money to find out if the phone is fixable or not.