This is Apple making it harder and harder to run apps that didn't come from the App Store (where Apple gets a tax on the software).
I've found references to it affecting most every popular app from Slack to Skype to Avid Pro Tools. Very few general answers on how to fix it. In some cases they say the developers fixed it, but I can find no pointers to how they did it.
Here is a summary of the suggestions I've found about what's happening and how to fix it:
1. The app is not installed in teh Applications folder. Just move it there and the problem goes away. Be sure to search for the app as it may be installed more than once.
2. It's traces of an expired digital certificate from an old install. Send the app to trash, search that there are no more copies, empty trash, then reinstall. In some extreme cases, people report having to use AppCleaner to get rid of all traces.
3. The app is owned by root rather than the user. Use a chown to fix that. e.g. https://apple.stackexchange.com/questions/267685/repeatedly-try-to-add-a-new-helper-tool-on-each-restart-for-same-applications
4. Some of these scenarios arise because people installed without being Administrator. Move all traces of the app to trash, empty trash, make sure you're logged in as Administrator, and reinstall.
5. Some say it is a Security option. Go to your Security tab and to it to allow non-App Store apps to run. Opinions vary on whether Apple even offers this option in later OS releases.
6. Some say it happens because the app accesses folders that require Administrator permission. The only folders it accesses are the app folder where it's installed and it's preferences folder. You can find which folder is preferences by going to Setup Files.
If you find a way to fix the problem on your machine, please let me know so I can help others!