I don’t think so. It doesn’t use the double ratchet algorithm used in DMs but still the participants of the group formulate a secret key for the group and share this key with every participant using the more secure protocol. The key cannot be read by the server as it is shared using conventional E2EE.

Refer this video from computerphile for more details. Start watching from 5:24. https://youtu.be/Q0_lcKrUdWg