I want to believe

The link for mandatory security rules links to rules for IAM, not networking.
https://docs.oracle.com/en-us/iaas/Content/Network/Concepts/networksecuritygroups.htm

But, apparently there are mandatory IAM policies, and the linked document skips the actual GUI procedure:
https://docs.oracle.com/en-us/iaas/mysql-database/doc/iam-policies.html

OpenStax offers free college textbooks

Prose Web application. XMPP client for team messaging. - prose-im/prose-app-web

This utterly failed when I tried to create a deployment of Nextcloud. Possibly it had to do with the template being from 2021, with Nextcloud version 23.

This is brilliant, complete with branded lens cap.

streamURL.link offers the stream URL for your desired radio station. Add the link to your media player like VLC, Windows Media Player, iTunes and more.

Genealogy websites can help you track down the records you need to build your family tree. Here are the best currently available for free.

The email looks decent. Worth the trouble?

5GB in free tier. WebDAV compatibility.

CalDAV & CardDAV tool for Linux/POSIX

Could I host a domain minus email?
https://docs.oracle.com/en/learn/oci_nextcloud_ampere_a1/index.html

freemium

Safe Android apps, available in the play store

Powerful Video Surveillance Software

compare to Shinobi

Music servier with Subsonic-compatible streaming

would it be worth running instead of Jellyfin? Maybe substitute a DVR-specific app that can stream and serve other video files?

See also: https://github.com/basings/selfhosted-music-overview/blob/main/README.md

There are many alternatives to Rhythmbox for Linux if you are looking for a replacement.

Audacious
Lollypop
Exaile
DeaDBeeF
Wora?

Low bandwidth & size limits, but there is a free tier. Probably pretty basic site builder.