It is extremely easy for a government to block / monitor a social media service which relies on a central server like Twitter, Facebook, WhatsApp, etc. They just block traffic to that domain and their citizens are cut off.
The two alternative types of Social Media networks are federated and peer-to-peer (P2P).
Federated means numerous different servers interconnect and transmit messages, so you can belong to any one of them and find your friends anywhere else. These include popular ones like Hubzilla, Mastodon, Friendica, Pixlefed, Peertube, etc all using ActivityPub protocol. Hubzilla even allows a nomadic backup node to be created ready for use. There are also networks such as Movim and others using XMPP Jabber protocol, and then also Diaspora.
Peer-to-peer networks have no central server or even decentralised servers with data on at all. They interconnect individual users' computers and each computer helps send data along to others. This is impossible to block unless you have all internet traffic blocked. Popular networks for this type are Secure Scuttlebutt (SSB), RetroShare, Aether, etc.
But joining after a government has blocked a network is a bit too late....
The govt through the Uganda Communications Commission (UCC) has reportedly requested all major telecom companies to