Matrix folks have some presentations on how this was done in the virtual events devroom here: https://fosdem.org/2021/schedule/track/virtual_events/.
Video from the first presentation here: https://www.youtube.com/watch?v=TzUfS08lMek&ab_channel=Matrixdotorg
π¦π: https://twitter.com/tgamblin/status/1359239300638908422