Organizations often hold large format events to build thought leadership, build brand, help build out the ecosystem and community and foster cross-pollination. The keynote talk is a format in which one person holds the attention to a large audience (100+).
This is hard to translate to a virtual format with the same energy and audience engagement. It can be done with some changes to the experience. The key is to use the webinar feature and not the meeting feature on the video conferencing platform (Zoom, WebEx, GoTo suite of products and the like).
In a webinar, the speaker would be well advised to separate their talk explicitly into the part that involves talking (20-30min tops), then Q&A.
The audience can ask questions (a feature not present in meetings)
And the speaker can also control whether attendees are permitted to talk (a must-have in a large audience situation!)