The government controls the algorithm? Then the government pushes propaganda.
The algorithm is public? Then what kind of public algorithm? "Sort by recency", "sort by popularity", etc. will be gamed by propaganda-pushers. "Sort by closest friends" is better, but I suspect even it will be gamed by adversaries who initially push genuine interesting content and encourage you to befriend them, then shift to propaganda.
Sorry to be cynical, but I doubt you can prevent people from being attracted to and influenced by propaganda; if necessary, well-funded organizations will hire paid actors to meet people in person. You must narrow the goal, e.g. can hinder foreign propaganda by down-weighting accounts from foreign IP addresses, detecting and down-weighting foreign accounts which use residential VPNs, and perhaps detecting and down-weighting domestic people who are especially influenced by foreign propaganda to the extent they're probably being funded (but you don't know, so then you get controversy and ambiguity...)