If you are ok with Jellyfin being public, then I would just put it in front of an nginx proxy. That way, your nginx proxy will handle SSL termination. With SSL, your ISP won't be able to inspect the traffic directly.

If you are running docker, then I'd recommend jwilder/nginx-proxy and its lets encrypt companion jrcs/letsencrypt-nginx-proxy-companion. It makes putting things behind an SSL proxy very easy! This of course assumes you have a public IP address through your ISP and aren't stuck behind CG-NAT!

A second option is to keep it private then use a VPN (this is what I do). Wireguard can be a good option although setting up each device is a bit manual, since you have to generate key pairs for each of them. This also requires you have a public IP through your ISP or have a public box that bridges your public VPN to your home network. That said, it works really well.

Tailscale is a free, but commercial option built on top of wireguard that makes set up a lot easier. If you are stuck behind CG-NAT this is probably your easiest option.

VPN is probably the easiest since you can use tools you're probably already familiar with, like RDP. But Guacamole is a pretty slick web interface for remote desktop to internal servers.

As far as encrypting jellyfin traffic, I'm not familiar with the specific details, but I imagine it has something similar to Plex where you check a box to require encrypted connections. With that enabled, the ISP can see that you're sending traffic over port X to IP Y, and how much traffic you're sending, but they can't see what the traffic is.

Probably the easiest solution would be to use Tailscale. Although it's not open source it is free.

Hosting a VPN is going to be the easiest and most secure option. There are a lot of little things that might make exposing Jellyfin tricky and could risk exposing traffic.

I would suggest starting out with a simple Wireguard VPN, which has worked for me for a while, but eventually you might consider looking at Tailscale, which simplifies a lot of it. (You can completely self host it using the Headscale server). OpenVPN has more options and its a little easier to add more devices, but it's not as fast.

I'm not sure if I'm understanding this one. But assuming that you're hosting your own server and you work away from home and want to connect in on the weekends. If you have https forced and it's also on in the app you're using to connect, any traffic between your end and the server is automatically encrypted. The only thing your ISP is going to see are data packets going from you to your server back and forth. Same if you're hosting for 10 users. All of VPN does is give you another point hop between the server and your client. Vpns are useful if you're trying to to block your ISP from seeing that you connect to a certain site on the internet. But just logging in remotely to your server it's absolutely useless.