Hello catalina,
The Mac operating system Catalina, includes lot of security features, Please check the link to know more about that – https://www.apple.com/in/macos/catalina/features/#security .
After installing, Start securing or decrypting/open your files with the AxCrypt app.
Please make sure that you have to allow the AxCrypt app to access the folders on your mac(refer the screenshot)
Still, you are facing any issues, please write an email and send the error report(ReportSnapshot.txt) file which is available in your system path(~/.local/share/axcrypt) with some detailed information in support@axcrypt.net.