Short version:

Currently, Microsoft allow only 300 users to be added to interactive meetings. They are increasing the meeting participant and chat size from 300 to 1000.  This feature rollout will begin mid-March and should be complete by mid-April 2021.

Details:

Currently, Microsoft allow only 300 users to be added to interactive meetings. They are increasing the meeting participant and chat size from 300 to 1000.

Look out for updates that allow 25,000 people in a team and another that will allow an additional 19,000 passive attendees in meetings…

Availability:

This feature rollout will begin mid-March and should be complete by mid-April 2021.