iPhone XS max "no service" after water damage.

With water damage, you have to decontaminate the entire logic board before doing anything else, otherwise there will be latent issues down the road even if you do fix it.

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

The proper way treat a wet phone is to do the following:

• Open your phone and remove the logic board
• Inspect the logic board, especially around the connectors and look for corrosion.
• Inspect both sides of the board. Unfortunately, pretty much all of the “logic” is hidden inside the logic board sandwich. 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 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 data/no fee policy so you don't have to spend money to find out if the data is recoverable or not.