I have this exact problem as well. Just purchased Parallels Desktop for Mac so I can run iPhoto, QuickTime 7 Pro, and other 32 bit apps on Catalina. Each time I try to open a photo in iPhoto or Photos on my Yosemite VM, I get a blank image even though the thumbnails appear correctly, and my libraries are not corrupted. This is November 11, 2023, so I guess the problems mentioned above have never been resolved.