Xcode error: The file couldn't be opened because you don't have permission to view it
I too had the same file permission issue to my existing project after updating to Catalina.
Resolved it by granting xcode the Full Disk Access.Got to
System Preferences --> Security & Privacy --> Privacy --> Full Disk Access --> Add Xcode & also in Files & Folders --> Add Xcode
Ok that was weird. I have not found a reason why this error occurred, but it's gone after I had created new project. The project was created successfully with all files loaded and after that all old projects started working fine. Tricky Xcode.