The default mode is not E2EE. The same key is used by all participants and is distributed by Zoom's servers. In this mode, all features are available, including the ones that require a cloud service (like 1-800 number support).

If a meeting is set to E2EE, then a bunch of features are turned off and the keys come from the host* and are sent to the other attendees enveloped with their public keys. Zoom's infrastructure never sees the keys, only the encrypted content packets that are relayed to all the participants.