Each 'devroom' has a different set of organisers, and it's up to them which talks they allow. There's a 'call for devrooms' in the Autumn of the year before, so someone could at that point propose a blockchain or cryptocurrency devroom.

There was in fact one blockchain-related presentation at FOSDEM 2024, in the DNS devroom: https://fosdem.org/2024/schedule/event/fosdem-2024-2198-the-...