It calls home if you register and you can get an idea of the sort of information it returns from here.
https://stats.moodle.org
The H5P plugin may call home with information.
If your question is related to privacy, Moodle treats it very seriously. If it is related to performance then there it is not an issue.

This is an excellent question that should really have some documentation. Items I can think of are:

- Checking for available updates for core and its plugins - on by default. (Setting and Scheduled task: Check for updates ). The endpoint seems to be https://download.moodle.org/api/1.3/updates.php.

- Site registration checks once a week if you are registered or not - on by default - even if you don't register, it still checks at stats.moodle.org. (Scheduled task: Site registration)

- MathJax is on by default and connects to https://cdn.jsdelivr.net/npm/mathjax@2.7.8/MathJax.js - even if you aren't using it. (Filter setting)

- H5P library updates, as Ken and Marcus note, are on by default. (Setting and Scheduled task: Download available H5P content types from h5p.org )


Things that may phone home or used to phone home but may not anymore but I'm not sure:

- Language pack updates - I'm not sure if or how these auto-update anymore or not? If memory serves (and it may not), there was a link for this on the packs page to do the update, but then it was automated to check for any new packs or updated strings in the installed packs. Is this true and if so is it part of the schedule update checks now or on its own schedule?

- Time zone file updates - Are these updated after install? I would think so since the tz definitions are not static and do change. There is no admin setting to update them. Ken, do you know how these are updated?


Randy