1) You can not protect users from being influenced by the media they consume-- that is basically the very nature of the thing.
2) This is not about protecting users of the app, this is about preventing a foreign state from having direct influence on public opinion.
It is obvious to me why this is necessary. If you allow significant foreign influence on public opinion, then this can be leveraged. Just imagine Russia being in control of a lot of US media in 2022. Or 1940's Japan. That is a very serious problem, because it can easily lead to outcomes that are against the interests of ALL US citizens in the longer term...
Isn’t that already happening? Fox news parroting russian talking points to sow division among the working class population of this country? Why is that fine? Because they get Rs in power in the process?
SCOTUS explicitly avoided ruling on this justification, and it seemed at argument that even some of the conservative justices were uncomfortable with the free speech implications of it.