I'm not sure who is pushing #GlobalSwitchDay probably won't amount to anything, some of these platforms are certainly not ready a massive migration. The #RedditMigration was rough enough on Lemmy, it actually murdered #Kbin; #loops #PeerTube and #Friendica don't have nearly enough well-maintained instances to support any sort of massive migration. And Signal, well its better than WhatsApp, and its mostly Free Software, but it doesn't really align with all of the others that are, or at least intend to be in the case of Loops, federated services based on ActivityPub.
Had to say that service != Software. The service indeed put restrictions, but, once released, loops can be perfectly libre software while keeping these restrictions within the service.