Fenix 6 screen issues after software update

You do not have a custom IQ watch face installed by any chance?

Something similar also happened to my F6x sapphire. Try to reset the watch by holding the light button(top left button) for approx. 15sec. It will turn off. Wait few swconds, then turn back ON again. If that doesn't help, try other reset option- turn off the watch, then turn on again, when the blue triangle appears-press and hold both right buttons. You will hear a beep, release the top button but keep holding the bottom button. Then you'll hear another beep- release the bottom button, that's it ! This method should definitely fix your watch !

Thanks for the tip but it did not work.

No

Another 2 options. 1. Wait until the watch will dicharge completely and will turn off. It will take some time... 2. Connect the watch to PC with cable. Then delete all the possible files -from Garmin watch. It will always keep the necessary files for functional working, don't worry, you can't delete too much !  Or, another option - upload manually software 24.10 from Garmin forum. And reinstall

Thanks for the new tip - I'm running down the battery now and will give it a try and let you know how I go.

Hey how did you go with this? 
same thing happening to mine and trying things to fix 

Your watchface definitely looks like a Custom Connect IQ watchface. So either the watchface needs an update or you change it back to a default from Garmin.

Thanks, but it did not work on my Fenix 6X Pro. I have this watch since Abril 2022 and it worked fine until now.

That looks like a hardware failure. In the OP's photo. Can you share a picture of yours? In the OP's photo, the display matrix isn't getting the right data. Best case, there is a flat flexible cable from motherboard to display that needs re-seating, which I don't recommend trying yourself unless you are confident/experienced doing that. Was the watch dropped?