When running a normal traceroute to your host, I'm getting a "Code: 13 (Communication administratively filtered)" ICMP error as an answer:
osiris@desktop ~ $ traceroute bardhome.de
traceroute to bardhome.de (79.244.37.18), 30 hops max, 60 byte packets
(...)
5 asd-s8-rou-1041.NL.as286.net (134.222.94.216) 15.299 ms 15.307 ms 15.994 ms
6 ae11-100-cr5-ams1.ipv4.gtt.net (194.122.122.98) 16.581 ms 16.595 ms ae16-100-cr6-ams1.ipv4.gtt.net (194.122.122.102) 17.366 ms
7 ae27.cr1-fra2.ip4.gtt.net (89.149.181.254) 23.749 ms 15.669 ms 16.291 ms
8 80.157.204.65 (80.157.204.65) 16.448 ms 17.277 ms 18.040 ms
9 p5b17dea1.dip0.t-ipconnect.de (91.23.222.161) 23.880 ms 24.514 ms 24.939 ms
10 p4ff42512.dip0.t-ipconnect.de (79.244.37.18) 30.559 ms !X 31.685 ms !X 31.927 ms !X
osiris@desktop ~ $
Those ICMP packets are originating from YOUR IP address, so something on your host is generating them, most likely a firewall.
If I'm tracing to TCP port 80, I'm getting a different error: "Code: 1 (Host unreachable)"
osiris@desktop ~ $ sudo traceroute -T -p 80 bardhome.de
traceroute to bardhome.de (79.244.37.18), 30 hops max, 60 byte packets
(...)
5 asd-s8-rou-1041.NL.as286.net (134.222.94.216) 12.936 ms 13.736 ms 13.741 ms
6 ae16-100-cr6-ams1.ipv4.gtt.net (194.122.122.102) 14.698 ms 15.039 ms 14.997 ms
7 ae27.cr1-fra2.ip4.gtt.net (89.149.181.254) 21.670 ms 15.962 ms 16.750 ms
8 80.157.204.65 (80.157.204.65) 16.309 ms 16.632 ms 18.591 ms
9 p5b17dea1.dip0.t-ipconnect.de (91.23.222.161) 23.859 ms 23.685 ms 24.274 ms
10 p4ff42512.dip0.t-ipconnect.de (79.244.37.18) 29.434 ms 30.605 ms 30.619 ms
11 p4ff42512.dip0.t-ipconnect.de (79.244.37.18) 3023.475 ms !H 3023.807 ms !H 3023.492 ms !H
osiris@desktop ~ $
Without nowing your exact setup, this is hard to debug. I'm seeing a docker0 interface, are you running Nextcloud in a Docker container?
Also, this probably isn't the best Community to ask this, as this most likely isn't certbot related at all, but a generic networking issue.