Hi! I've been having this problem in the past couple of weeks, where my layers do not show the content properly and are no longer transparent, but instead they do this (see image below/attached).
They used to be transparent and show the content more clearly. I don't recall having done anything to make it change, except update to the most recent version of Photoshop CC 2020.
Is this a bug, or something I can fix? It's very frustrating when I'm trying to go through what I've done!
Is the Transparency Grid still being used on the Canvas when you hide the Background Layer?
I didn't think to check that until you asked.
No, the transparency grid doesn't display.
What are the Photoshop > Preferences > Transparency & Gamut settings?
Yay! This was indeed my problem. I don't know how that happened to end up like that, but it's fixed now.
Just a »stab in the dark« but does turning off »Use Graphics Processor« in the Performance Preferences (Photoshop > Preferences > Performance > Graphic Processor Settings) and restarting Photoshop have any bearing on the issue?