Presently, Loom will only accept a calendar feed with invites to upcoming meetings as what causes a meeting to be recorded.
This is a real problem as often recordings arrive after the fact. Also, some meetings are recorded as audio-only, e.g. in the event of poor internet connectivity.
This inflexibility impacts many things, not least in making the case that it would be straightforward to migrate to Confluence and Loom from a competitor product.