I've been trying to upgrade from 10.10 to 10.11 for a while now, as the Android TV app keeps nagging me, and every attempt ended with impossibly long library scan times.
After some thorough investigation, it appeared that a Home Videos type collection causes unending scan (yet to be solved), but also that Jellyfin does a lot of writes to the config directory (either database or metadata or both). Mine's on spinning media part of a ZFS pool. I tried a few performance tuning options, such as testing the config dir with recordsize (similar to block size) of 4K, 8K, 64K, 128K and library scans fell from 30-40 minutes down to 8-13min with 4K-64K. The ZFS tuning wiki suggest 64K recordsize with LZ4 compression for SQLite workloads such as Jellyfin. That seems to work as well as 4K and 8K but likely is faster when reading thumbnails and such.
Note that upgrading to 12-rc3, which is supposed to speed up library scans did not improve scan times for me. Optimizing config/database write speed did. I cross-checked the culprit by experimenting with moving the config dir to NVMe and RAM. Both of those got the scan times down to 8-9 minutes compared to the optimized spinning media's 12-13.
So if you had upgraded (or about to) to 10.11 your library scans are (about to get) dog slow and your Jellyfin's config dir resides on spinning media, optimize its write performance for SQLite.
Doesn't jellyfin need a static IP.
Static IP for what? As long as you know the ip address of your jellyfin server you can connect to it. A static IP is just good to have for ease of remembering, using your own domain (not that you can't do it with Dynamic addresses) or if you are integrating other services with it. This applies to any service you host.
Most ISP connection are behind CGNAT(ipv4), and in case of ipv6 to have a secure connection wouldn't that require SSL certificate and a domain?
You could use tailscale or netbird. Alternatively, you can use a dynamic DNS provider which usually provide free subdomains, if you don't want to pay for a domain. And even with all of that, Jellyfin doesn't require HTTPS, although there may be clients that do (make sure you're behind a VPN in this case).
I have Pangolin setup on a VPS so I and my family can access it externally. It "bypasses" my router's firewall. Tailscale was a stupid solution because a lot of people will be using it and I don't want to maintain another service and be tech support for their tailscsle client. So the only thing I did to restrict access was by geoblocking.
Jellyfin expects you to actually host it yourself, instead of baking in a proxy and selling you the service.
There are plenty of free subdomain providers, and let's encrypt gives out free certs.
If you're not hosting through a VPN you should consider those a requirement so you're not sending an unencrypted password to your jellyfin instance over the internet. Regardless of your ISP situation...
No.
To function? No.
Useful? Yes.