Catalina Photos location messed up

This is a change in Catalina. Photos does no longer store the originals in the Master folder in nice subfolders, named by the date of the Import session. The files will be renamed, randomly, so we cannot find them by searching for the filenames, the dates of the original files are changed, some meta data may be stripped. To get your original files back out of Photos 5.0 you have to use the command "File > Export > Export unmodified originals" and save a copy on an external file. I recommend to back up all originals before you import them to Photos, so you can save the original file creation dates and all metadata tags.

For an emergency access to the original image files you could use the application PowerPhotos. The free trial will suffice for this. When you browse your Photos Library in PowerPhotos and select a photo and ctrl-click, you will a command "Reveal in Finder". This will show you the cryptically named original. But the first launch of PowerPhotos takes a long time; I am always launching when I start working with Photos, so it will be ready when I need it.