Your webserver, when requesting http://xn--derwscheladen-efb.at/ redirects to https://www.derwäscheladen.at/.
While the HTTP to HTTPS redirect usually isn't an issue, the punycode to IDN translation is, as IDN is not directly supported in DNS, but needs to be translated to punycode.
Also note that your certificate doesn't include the "apex" domain name, but only the www subdomain. You might want to include both.
Creating the certificate was done by someone else, and I just watched. But from what I know, there was initially a problem, and we had to try it again. I believe it had something to do with the "Punycode" or the "ä". Is it possible that these are the two certificates, and the non-functional one is the one that couldn't be created?
Okay, thank you. How should I proceed now? Does the website remain certified due to the functioning certificate, and should I just leave the non-functioning certificate as is, or what should I do?
Your cert for that domain was renewed but your Apache is not yet using it. You probably need to reload Apache. This should work: apache2ctl graceful
You should use cron to reload Apache daily or we can adjust your certbot renewal to do it every time the cert is renewed. Let us know what you prefer.
As for your "broken" renewal file that you say is empty you could just delete that renewal conf file. You can't use the normal certbot delete command because it is broken so just delete it manually.