Anti-Foos already think that real primary Foo sources are nonsense (and they aren't the target audience anyway), and confirmation bias will take care of the pro-Foos.

If it's not moving opinion, it's not effective propaganda. Something that people will agree with only to the extent it restates what they already believe isn't working as propaganda.

Not sure I agree. Some propaganda probably just wants to rile up the base.

It's also possible to change which issues seem most salient/urgent/etc. without actually changing anyone's mind. E.g. Democrats typically care about police brutality, and the environment, but they probably thought more about the former a few years ago and the latter more in 2019, even though AFAIK the actual issues haven't changed much.