When using the new Banktivity (version 8 or 9), the Banktivity ID password should be saved in Keychain Access on your Mac. Keychain Access is a utility application located inside the Utilities folder on your Mac, the Utilities folder is located inside the Applications folder – /Applications/Utilities/Keychain Access
From Keychain Access use the search field to search for:
Double-Click on the listing for ‘com.iggsoftware.service.authentication’, then from the window that appears, place a checkmark beside “Show Password”. Enter the Login/Admin password for your Mac (this should be the same as the password you use when your Mac starts up). Then you should see the encryption password.
Also, in Keychain Access you should see “Account” displayed when “com.iggsoftware.service.authentication” is selected. The “Account” in Keychain Access would be the “Login ID” for your Banktivity ID account. (this may or may not be your email address)