After downloading Xcode 11.3 (twice), I keep getting this message when I try to build any of my existing projects:

The file “Preview Assets.xcassets” couldn’t be opened because you don’t have permission to view it.

I've used "get info" to check the permissions for Assets.xcassets. Even though the permissions looked good, I changed them again. I also tried:

• other solutions for this problem from earlier versions
• deleted and re-added the Assets.xcassets files
• re-booted my Mac
• deleted and reloaded Xcode