In case it wasn't already known...
It seems like Photoshop CC 2018 (sometime in the last six months, maybe) isn't compatible with Encore CS6.
At the end of last year, I was able to right-click a menu and Edit In Photoshop.
I tried, yesterday, and it said that Photoshop wasn't installed.
After some light troubleshooting, I installed Photoshop CS6 and all was right with the world.
If this was a designed, failure, that's fine.
If it is still supposed to work, then something needs to be addressed.
I'm not sure about compatibility, but have you tried reinstalling Photoshop CC 2018 to see if Photoshop appears in Encore?