Is there a way to tell what rooms or how many people are using a particular video bridge? Is that in a log, REST API somewhere?
You can get a lot of stats, including number of participants, conferences, etc. on that bridge.
in addition to the doc that @yasen linked to, there is also the undocumented debug interface.
curl http://127.0.0.1:8080/debug | jq
→ list meetings with their ID
curl http://127.0.0.1:8080/debug/<meeting-id> | jq
→ gives details for a (running) meeting