Thank you very much for the quick answer. I installed certbot 2.7.4 with pip right now (thanks for that hint!), it's not yet working, but I'm making some progress.
Renew failed with this:
Hint: The Certificate Authority failed to download the challenge files from the temporary standalone webserver started by Certbot on port 62080. Ensure that the listed domains point to this machine and that it can accept inbound connections from the internet.
Probably the syntax to define the port number changed, in October it still worked:
sudo /usr/bin/certbot renew --http-01-port 62080
I'm going to look into the certbot Docs or ask Dr. Google perhaps he knows..
Additional info, a dry-run worked
sudo /usr/bin/certbot renew --http-01-port 62080 --dry-run
...
Congratulations, all simulated renewals succeeded:
/etc/letsencrypt/live/kriebel.mooo.com/fullchain.pem (success)