After using Franz for a couple of years, I can no longer sign into Google Mail. The message says:
"This browser or app may not be secure. Try using a different browser. If you’re already using a supported browser, you can refresh your screen and try again to sign in."
The Learn More link is https://support.google.com/accounts/answer/7675428?hl=en-GB
There is information in this link for App Developers on how to change their app to meet the new standards.