Problems with installation of Desktop Client

Good day!
I have windows 10 and formerly used already NC Client for Desktop on my Dektop-Computer.
Recently I had to do restore system in windows.
So Nextcloud was deleted too.
Now everything works fine and I also want to reinstall NC Client for Desktop.
The installation process is working without problems.
However, it is not possible to connect with the server.
Whenever I type the serveraddress I get the information: Host www.xyz not found, no connection possible
(“Die Verbindung zu Nextcloud auf https://www.xyz: Host www.xyz konnte nicht gefunden werden konnte nicht hergestellt werden”)
I repeated all the procedure with same result.
What can I do?
Thanks!

Can you login with browser?

Yes, this is not a problem!

Propably a false positive bruteforce attack?
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