How can I track how embedded media is used across my site?
First, there is a core issue to eventually get this into core.

Now, the best way is to use the Entity Usage module, which can handle tracking of media and many other cases.

Hats off to the module maintainers-- this is all I needed to do to implement my use case:


Download the module with composer.
Enable the module.
Go to /admin/config/entity-usage/settings and check Media under Enabled local tasks.