Welcome @knoppid
The EFF is discontinuing support for Windows in Certbot starting next month. You should not use it for new Windows installations.
See below thread for suggested alternatives. The problem you are having is that Certbot is not well integrated into the way Windows shares ports. One of these Windows-specific alternatives will work better.
For Jellyfin, you might even consider a proxy like Caddy which manages the certs for you. I saw that mentioned in talks about Jellyfin when I searched just now. In fact, here is a how-to from a dev of caddy on the Jellyfin forum (link here)