I'm selling my Apple Watch Series 4 LTE, running WatchOS 10.
As you can see, the screen is shattered, but I added a full cover protective case and I've used the watch this way for months without any problem. Everything fully works and the touch screen also functions perfectly as intended.
I would not put it under water since the glass is shattered.
Battery health is at 76%, so not the best but enough for a day if you charge it at night.