Your LimeSurvey version: LimeSurvey Community Edition Version 5.6.37+230905
Own server or LimeSurvey hosting: Own, Debian, Apache 2.4.56, PHP 7.4
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The Comfort Update says: Fehler: Keine Server-Antwort! (Error, No server answer!)

What can I do?
Best

Best thing is to wait a few hours and try again. If the server in not reachable after 48h I would ask the LimeSurvey support via ticket.

It not that seldom that the update server is unreachable for an hour or two.

Man, when there is a university that is actually trying to stay up to date (kudos to the admin on that install!) the update server is down. Hahahahaha.

But like Jelo, it can happen that the server for Comfort Update is down or has temporary connection issues. I would wait a couple of hours and try again. And if it doesn't work over a longer period of time, open a support ticket with the Limesurvey GmbH. At the end, you are a paying customer of Comfort Update.