http://kb.mozillazine.org/Password_Manager was written for Firefox but should apply to Thunderbird. Passwords are currently stored (encrypted) in a logins.json file in the profile.
I suggest you restart Thunderbird and look in tools -> options -> security -> passwords -> saved passwords to see if it has your app password before worrying about the config editor settings. Those settings only matter if it isn't stored by the password manager. On my system searching for signon in the config editor returns default values (not bolded) for everything except signon.importedFromSqlite
If it is stored okay but not automatically used see if the problem is due to a theme or add-on that doesn't play nicely with the current version by using "help -> restart with add-ons disabled"
If you can't get the built-in password manager working I used KeePass with the KeePassHelper add-on (needed to help it recognize the right windows to enter the password) a couple of years ago as an experiment. It worked fine. The Add URL to Window Title add-on also used to do the same thing but it now only supports Firefox.
https://addons.mozilla.org/en-US/thu...er/?src=search
https://keepass.info/