file can't be opened because it is from an unidentified developer

Hi MrHoffman

Thanks for the pointers. Here is what I can report.

On my computer and my user configuration .tif and .tiff files are set to open with Photoshop and .jpg files are set to open with Preview.

• If I set a .tif or .tiff file to open with Preview (using Finder Get Info panel), then I get the "can't be opened" warning when I double-click on the file.
• (I am not going to System Preferences to allow the files to open while doing this testing.)
• If I set a .jpg file to open with Photoshop, I get the same warning.
• Sometimes the file will open once in the indicated application after changing the default app, but after that I always get the warning. I think this might be a timing issue, as it might take time for the default app setting to propagate to all parts of the OS.
• I get the same behavior with files on my internal drive (FileVault) and my external drives (SoftRAID RAID-5 with no encryption)
• If I create a new user, then for that new user, Preview is the default app for .jpg & .tif files, because this is how a new user is configured.
  • If as user 1, I set the default app for a .jpg file to Photoshop, and then copy the file to /Users/Shared, and then as user 2 copy the file from /Users/Shared to ~/Desktop, the setting for the default app is preserved, and I get the same "can't be opened" dialog if I double click on the file as user 2.
  • If as user 2 I change the default app for this .jpg file back to Preview, I can open the file by double-clicking
  • If as user 1 I copy a .tif to /Users/Shared, and then as user 2 copy the file from /Users/Shared to ~/Desktop, the file comes over with Photoshop as the default app to open it. (This is because all .tif's for user 1 should open with Photoshop, and when copied to user 2, the file is set so that this file (but not all .tif's) has Photoshop as its default app. In other words, when I copy a .tif from user 1 to user 2, it comes in with the same settings as the .jpg mentioned above: the default app for the file type is Preview, but the default app for this file is Photoshop.
  • And when I double click on this .tif, I get the same behavior as above--the OS tries to open it in Photoshop, and then gives me the "can't be opened" dialog.
  • If I set the default app for this .tif back to Preview, then it will open normally (because for user 2, Preview is default app for all .tif's).
• If I (as user 1) set the default app for a .tif file to Preview, but then right click on the file and open the file in Photoshop, then I get warning that otherwise is shown by System Preferences::Security & Privacy::General when I try to override the "can't open" warning. But in this case the warning is shown when I first try to open the file, not when I go to System Preferences to override the warning.
• The source of the file does not matter. I have seen this for files sent by Dropbox, files downloaded as part of a .zip from Google Drive via Firefox, and for files that were created in Photoshop.
• Unless I am mistaken, the only apps that have deep control of my computer are SoftRAID, Little Snitch, and Dropbox, but I'll post the EtreCheck in the subsequent reply. No VPN clients, no cleaner apps.
• I have seen this for other file-type + default app combinations. For instance, on my computer .rtf files are set to open with NisusWriter. If I set a particular .rtf to open with LibreOffice, I get the same warnings, and have to override at System Preferences::Security & Privacy::General.

Reminder, I am still using Mojave. But I have seen this problem with earlier iterations of MacOS, on earlier computers. On 2019-08-24 I erased my internal disk, installed a clean copy of Mojave, and restored from a Time Machine backup. (I had files in the trash that couldn't be deleted, and I just wanted to be sure that any "cruft" from earlier installs was hopefully removed).

I'm putting EtreCheck output here.

TIA for any help you can give.