In BBB (BigBlueButton), to see live transcription, those speakers (instructors, helpers, etc.) must have such enabled otherwise such cannot be in BBB. Simply click on the CC icon on the left to view that text.
That said:
If you are using the Chrome web browser, you can enable captions in the Chrome web browser on your computer/phone, see this link from Google. (This has been supported in Chrome since 2021 and can be handy to use when transcriptions are not otherwise available.)
If Zoom and not BBB (BigBlueButton) is being used in the course, Zoom supports live transcription in its application (if you are using a new enough version). If you cannot see it in that Zoom session, then ask for it to be enabled in that Zoom session.
