Most of the discussions will take place using Matrix. This blog article explains more on the topic:
https://matrix.org/blog/2021/01/04/taking-fosdem-online-via-...
https://matrix.org/blog/2021/01/04/taking-fosdem-online-via-...
* https://fosdem.org/2021/schedule/event/matrix_communities/
* https://fosdem.org/2021/schedule/event/jitsi_scaling/
* https://fosdem.org/2021/schedule/event/vircadia/