If you need to explore alternative videoconferencing services, the following may help you. This information is up to date as of March 01, 2021.
Zoom supports both free tier, integration support, closed captions and API for 3rd party captioning.
RingCentral supports free tier, integration support and closed captions. No API for 3rd party captioning.
Webex supports free tier and integration support. No closed captions support was found!