During my first three years of snorkeling I used a waterproof bag for a smartphone camera and a snorkeling set which you can see on the photograph below.
Sadly, the bag directly pressed against the touchscreen. The Baltic Sea is salt water and so the touchscreen felt touched everywhere. I solved that problem by building a frame for the smartphone inside that bag. With this frame there is always a bit of air between that bag und the screen and I can press the material onto that surface.
The approach had two other problems. The bag was stressed too much so it got broken every year, and also I wanted better quality. Since 2019 I have a waterproof camera. I will add details later.