got his message "destination folder is not writeable" on a Mac OSX 15.1.1. LR 14.1

The online search result you posted is labeled an “AI Overview.” Although those can provide insight, they are often not completely helpful. In this case, it isn’t because the AI answer is wrong, but because it’s incomplete. I often scroll down past the AI suggestion to find possible solutions posted by actual humans.

You aren’t wrong to check the traditional Unix file permissions at the bottom of the Get Info dialog box. That’s one way to restrict folder access in macOS that goes back to the beginning of Mac OS X.

Another way is to check if the Locked option is enabled in Get Info, but your screen shot shows that’s OK.

But the third way is in macOS System Settings: Full Disk Access, and Files & Folders. Because it’s relatively new, introduced several years ago, it’s something the old macOS/Unix veterans don’t always think of, and apparently it also isn’t given proper weight by Google Search’s AI, so it failed to bring this to your attention. If you checked the Info panel and those options didn’t fix a Mac permissions problem, then you go on to do this.

Start in System Settings / Privacy & Security.

Then look at both Full Disk Access and Files & Folders. It’s easier to just grant Full Disk Access to Lightroom Classic. If this is done, then Files & Folders is not editable because it tells you that the application already has Full Disk Access. If you don’t grant Full Disk Access, then at least in Files & Folders, grant access to the application for the specific folders that you want to let the application have read/write access to, but then you have to remember folders like the settings folders for the application; it’s easier to grant Full Disk Access.

I have heard that sometimes you get these types of permissions errors even if these macOS settings look like they’re set correctly, possibly because of macOS bugs. I haven’t dealt with this myself but if that’s the case, I’ve read that one possible way I’ve read to fix it is:

1. Toggle those macOS Privacy & Security settings. 

2. Restart the Mac, and see if that clears it up. 

Another possibility: If the folder it’s trying to write to is not on the startup volume, in the Finder look at the bottom of that volume’s Info window and try selecting Ignore Ownership On This Volume.

It's likely that an Apple MAC OS update changed the destination permissions. This Apple article should help you with that.