I posted this in another thread but wanted to make sure people saw it. I don't think this is a real "fix" for this problem, but it worked for me, and it should work for you too.
There's another folder containing app info. You need to add permissions to this and the subfolders. Not sure why this requires specific user-level permissions now, it did not in the past AFAIK.
Note: you will need to ensure the permissions are correct per the previous solution article before you do this (except for step 4 - creating a new admin account. Don't do that!). If those aren't correct, and you only do this piece, Lightroom still won't work.
1. In Finder, go the menu bar and click Go > Computer (or Shift - Cmd - C). Then go to your HDD (could be something like Macintosh HD) > Library > Application Support
2. Right-click Adobe folder, and select "Get Info". Or, highlight the Adobe folder and type Cmd-I.
3. Authenticate to the folder by clicking the lock icon at the bottom right of the Info window.
4. If your user name is not in the Sharing and Permissions list, click the Plus sign at the bottom left of the Info window.
5. Then select your username from the list and hit OK. (If the Plus sign is grayed-out, you did not authenticate correctly in the previous step.)
6. Ensure your user has Read & Write permissions to this folder. Under Privilege, select Read & Write next to your user name. (If you just added your user in step 4, your user will only have Read Only access).
7. At the bottom of the Info window, click the Gear icon, then click "Apply to Enclosed Items". You will get a dialog asking if you are sure. Click OK and it will adjust the permissions accordingly. You can then close the Info window.
You should be able to start Lightroom now.
My guess is that this is a workaround instead of a real fix. Users don't normally get Read + Write access to the /Library/Application Support folder + subfolders. But it gets me back into Lightroom for now.
Thanks. Will Try.