Mozilla Thunderbird 45.8.0 in the "Create account dialog", it will never be able to connect to my email-provider

Mozilla Thunderbird 45.8.0 from rapps
in the "Create account dialog", it will never be able to connect to my email-provide

It worked in the past, but does not longer, so I do expect that to be related to encryption / certificates or cipher support. I don't think that it regressed in ros source code though, more likely that the provider may have dropped some fallback support during the last year.
I used an account xxx@gmx.de

I don't want to share my credentials so you will only get a video of that initial dialog.
I tried to
connect via POP3 without success
I tried to do IMAP without success
I tried unencrypted, without success.
Everytime I press the button "Erneut testen" (translation to english "retry the connection") Thunderbird will tell me that "Thunderbird konnte keine Einstellungen für ihr E-Mail-Konto finden. " -> english translation: "Thunderbird could not find the settings for your email account".
0.4.14-RC-128-g33e492a_Thunderbird45_8_0_affected.log
0.4.14-RC-128-g33e492a_Thunderbird45_8_0_affected.webm

This renders the application useless currently.