If it works, I don’t update unless I’m bored or something. I also spread things out on multiple machines, so there’s less chance of stuff happening like you describe with the charts feature going away. My NAS is pretty much just a NAS now.
You can probably backup your configs/data, upgrade, then deploy jellyfin again, restore, and reconfigure. You should probably backup your data on your ZFS pool. But, I recently updated to the latest TrueNas Scale from ~5 year old FreeBSD version of TrueNas and the pools still worked fine (none of the “apps” or jails worked, obviously). The upgrade process even ported my service configurations over. I didn’t care about much of the data in the pools, so only backed up the most important stuff.
NFS gives me the best performance. I’ve tried GlusterFS (not at home, for work), and it was kind of a pain to set up and maintain.