Nextcloud is federated? First time I hear about that.
For me it’s Lemmy, without a doubt. Never used Twitter, tried mastodon to see what it’s all about, didn’t like it.
Matrix seems decent, but nobody I know uses it, and finding useful groups is painful, especially on other instances (servers, whatever they call them).
That’s all under the assumption that Iran didn’t secretly develop nukes, or bought them from Russia or North Korea and just keeps it completely hidden to turn the tides at the last possible second.