Hey ladino, just to update you (as requested) this should be fixed now.

The version currently available at https://www.fatpick.com/downloads/FATpick-mac-latest.dmg is fully notarized by Apple and should not have this problem.

Release notes here: https://www.fatpick.com/blog/release-notes-fatpick-v1-4-2

Please let me know if you encounter any problems with this new build. You can reach me via the contact form at https://www.fatpick.com/contact-us or you can email me directly at rod@<that-domain>.

The app is code-signed with a valid Apple developer ID, but you may be seeing problems because it is not directly distributed through the app store. Per Google apparently a lot of apps have run into this problem: it seems that post-Catalina Apple insists on an additional "notarization" step for non-store apps. I was actually aware of this general problem since there was some hubbub about Electron 7+ apps having issues with that process, but I mistakenly believed I was immune to that problem by pinning to Electron 6. I'll ping you once we've jumped through that hoop, but unfortunately it isn't something that I can fix instantly.

In the meantime you can make an explicit exception by "right-clicking" on the application icon and selecting "Open" from the context menu that pops up.