Hi, mach751, I’m going to ask you a dumb question right off the bat. Are you running/do you have Catalina ( macOS 10.15) on your MacBookPro 16”? You can find that out by going to “About This Mac”. If you are, the default setting for it is “read only”( at least for your internal hard drive/ssd). To change that, click on your hard drive/ssd icon on your Desktop once, so it’s highlighted, then press Apple+I keys on your keyboard ( do a ‘get info’ on it) and you should see a long window, sharing and permissions should be about halfway down… to make any changes, click the lock at the very bottom of the window, and type in your login/admin password when asked to, the lock should unlock, go up to the sharing and permissions part of the window, there should be 2 columns: user on one side, permissions on the other side, you should now be able to change it from “read only” to “read and write” for all users. When you are done, click the lock at the bottom of the window, that should be it… close the window and try to open the jpeg file…
John B