I had entered some incorrect ports so jelly was stuck for a while until eventually ERR_CONNECTION_TIMED_OUT.

If, since there is no loading indicator, you click again before the connection times out, the app crashes.

https://github.com/jellyfin/jellyfin-media-player has a section "Client Settings" in the settings as seen in this screenshot:

For me especially relevant is the ability to bitstream what is called ac3 in the screenshot, which jelly does not seem to do automatically right now.

Maybe there is need for a whole client settings.

jelly-desktop W: .INSTALL file runs a command provided by hooks.

update-mime-database /usr/share/mime || true
update-desktop-database /usr/share/applications || true

Are the one not necessary, while link creation can be done in the pkgbuild

jelly-desktop E: GPL-3.0 is not a common license (it's not in /usr/share/licenses/common/)

license typing is GPL3 in Arch packaging, an fpm artifact?

group = default

not needed, an fpm artifact?

jelly-desktop E: File (usr) is owned by 0:0
jelly-desktop E: File (usr/share) is owned by 0:0
jelly-desktop E: File (usr/share/icons) is owned by 0:0
jelly-desktop E: File (usr/share/icons/hicolor) is owned by 0:0
jelly-desktop E: File (usr/share/icons/hicolor/128x128) is owned by 0:0
[...]

All files are owned by 0:0, from the Archwiki

# npm gives ownership of ALL FILES to build user
# https://bugs.archlinux.org/task/63396
chown -R root:root "${pkgdir}"

https://wiki.archlinux.org/title/Node.js_package_guidelines#Using_npm

Like the classic streaming service "who is watching" screen on startup, including selection between users across multiple servers:

• save multiple server details
• save multiple logins (per server)
• account switcher similar to the netflix ui etc

The old app https://github.com/jellyfin/jellyfin-media-player has this.

I had entered some incorrect ports so jelly was stuck for a while until eventually ERR_CONNECTION_TIMED_OUT.

Meanwhile the app goes to a black screen.

The announcement info includes no port, at least in my case.
It probably makes sense to assume 443 when it's a https address? Maybe even 80 when plain http?

If you think that assuming the jelly default port still makes more sense, then perhaps try these ports if the jelly default port doesn't work.