> Error: /Users/tzs/Library/Biome/streams/restricted/ProactiveHarvesting.Mail/local/91257846325132: Failed to open file: Operation not permitted

but when I check that file I have no trouble opening it. I can't see anything in the permissions of it or any of the directories on the path that would permit opening it.

Then I'd have to search the net to find out what the heck that is and whether or not it is safe to add an exclusion for it or for one of the directories on the path.

I eventually figured out that before searching the net what I should do is create a new backup plan and take a look at the exclusions in that new backup plan. Often I'd then find that there is a default exclusion that covers it. (In this particular example ~/Library/Biome is excluded by default).

When they update the default exclusion list that is used for new backup plans it does not update the defaults in existing backup plans. Evidently either Biome did not exist several years ago when I made my backup plan, or it was not a source of errors and so was not in my default exclusions.

So now I occasionally create a new backup plan, copy its default exclusions, delete the new backup plan, and then compare the default exclusions with those of my backup plans to see if there is any I should add.