Could you please fill in all of the fields in the help template? When you submit a new help request on this forum, a document should appear with a number of questions related to your configuration. Having all of that information will help people here to help you.
I’m using i-MSCP as my ACP.
When I add a new domain or subdomain, I have to run certbot --apache certonly in order to renew the certificate for the freshly added domains. But if I do so it tells me that it’s unable to find a vhost and that I have to select one so I try to use host.kazuto.de because this is my host, but giving me an error afterwards.
Do you have multiple VirtualHosts defined in a single configuration file within /etc/apache2? The current version of Certbot cannot handle this situation correctly, yet very often fails to warn about it.