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.
None of the reddit user diasporas made a dent on reddit's usage, but people did start using other platforms.
Like tiktok's ban: it's not going to move people anywhere else because most people have multiple social media accounts thanks to marketing and that's what this is.