There is a problem with JPEG images that were not created with Photoshop, but are then changed to be associated to Photoshop (macOS Get Info box, change Open With to Photoshop). Once you make that change and double click the file, you get an error like this:
“afterwork_2560x1440.jpg” cannot be opened because it is from an unidentified developer.
macOS cannot verify that this app is free from malware.
You can still get around the error to open the file but it becaomes a problem when you have to process multiple files and deal with the error repeatedly. If you change the file association to an app like Preview, then you can open the JPEG without the error (you just can't double-click it to do that). Something is wrong if Photoshop thinks a JPEG image is an app. Even if I create a screenshot of my mac, which creates a PNG, and then I open it in Preview and save to JPEG, then change the association to Photoshop, it yields the same error.
Running macOS Big Sur, but I've seen it in earlier OS's.
»Something is wrong if Photoshop thinks a JPEG image is an app.«
The message appears to state that the OS that »cannot verify …«, not Photoshop.
Which application was used to create the jpgs?
Can you provide one?
I don't know what app created the JPEG's because I was given them for a project. But it doesn't seem to matter where they came from and who made them as long as it's not Photoshop. If you follow my intructions above to make a screenshot and then save it as a JPEG, let me know if you encounter the problem too. And then when you do get the JPEG open in Photoshop and then save it, the problem is also gone.
My understanding is that Photoshop attempts to open the file but it is somehow flagged as suspicious, which macOS then reports to you in the form of the error dialog.
No, your understanding is not correct. When you double click a file, it is Finder that makes the decisions. If something is an app it looks for a special signature. It is confused for some reason. Photoshop is not involved in this process (presumably - you can confirm this - by leaving Photoshop not running and seeing that it does not start).
I'm not saying it isn't a serious problem, but it's always helpful to know where NOT to look for a solution.
I agree to a point. Photoshop is involved, but only to the point of letting macOS know that it can open JPEG files. macOS seems to be confused when Photoshop is not the default app to open JPEG's. I discovered this today through testing - if you change the system default to Photoshop then the problem goes away. I did nothing else except that, and all the previous files now opened without error.
Something in macOS is incorrectly flagging these JPEG files if you manually change them to open in Photoshop, rather than make it the system default.
Actually, I wonder if there is an old version of Photoshop somewhere on one of your disks, and you have accidentally told Finder to use this old version which won't start in Big Sur...?
Photoshop 2021 is the only version of Photoshop on my system. 2020 was the first version I had installed about a month or 2 ago, then I switched to 2021 and unstalled 2020.