I am looking at https://rocket.chat/docs/user-guides/voice-and-video-conferencing/#voice-and-video-conferencing
It sounds like there is no audio-only conferencing option, just a video conferencing option?
You could use Jitsi with just audio, just don’t turn on the camera. But yes there is no Audio only dedicated conferencing feature that I am aware of that isn’t linked with the video chat features.