Having downloaded 2.9.5 Mac which didn't work I went back to 2.9.3 which now does not work either. Both versions now say that there is an error/corruption, please delete. So everytime I try something different, the same error message. NOW NOTHING CURRENT WORKS!!
2.9.5 kept crashing on me the first time I opened it. It took multiple rounds of open, deal with error messages, crash, reopen before it finally got its pants on straight. Now it's running pretty well, though obviously still beta software.
It should have saved a copy of your pre-2.9.5 data in ~/Library/Application Support/openlp. Just rename the current "Data" folder to something else (or delete it), and rename the "Data-YYYYMMDD-HHMMSS" folder to "Data" so that the old version can find its old data.
The corruption error is a known issue, see https://openlp.org/blog/ for the fix.
It's not actually a corruption, it's Apple trying to prevent people from installing software on their computers that Apple hasn't sanctioned.