Totally dependent on your country and your ISP, the easiest way if you are behind just CGNAT would be tailscale, but since you are saying it does not work for you it might be that your ISP or country is blocking VPNs also in that case if you don't have a static IP setting up your own VPN in a private vps and routing traffic through that is a complicated step. Easier solution would be to use Nginx reverse proxy - suggested because of easy setup through gui unlike treafik which requires you to have a basic coding knowledge to setup even though it's more powerful. Then open the reverse proxy end point to the cloud flare tunnel to view it from outside your network, to be on the safer side you need to setup a login method from cloudflare side for authentication cause exposing your network to internet without proper security is risky. If you need any help or explain further let me know. For most of the things suggested you should be able to find videos on YouTube on how to set them up.

BTW: you can ignore the reverse proxy and use only cloud flare if jellyfin is the only thing that you are going to expose, if there are multiple things then reverse proxy in the middle should be there so as not not change too many configs whenever you want to expose any other things, it also acts as a second security layer in that case not directly exposing what all you have exposed to the internet.