If
1) just one person posts it, and
2) it is displayed in a literal reverse-chronological timeline, and
3) displayed only to the people who directly follow them,
then yes.
But, as soon as FB starts analyzing it, curating it, and using their humans or algorithms to promote, amplify, or extend the spread of it, FB becomes responsible.
That item has been selected, curated, approved, and amplified by FB, by their criteria, whoever first posted it (whether the post was from a truly organic FB member, a RUS dezinformatsiya shop, a FB employee, or some other source is irrelevant at that point).
This is no less responsibility than a news editor choosing which of their reporters' stories, or newswire stories to publish on the front vs 17th page, or run at the head of the national news, or just send to the local stations to run as they please.
The editors didn't write the content, but they DID curate, select, and selectively amplify (or de-amplify) it.
FB has the freedom to curate and amplify what they choose for their own purposes.
It is long past time for FB to live up to, and be held to, the responsibilities of their editorial actions (regardless of the level of automation - it's FB's algos, not the users').
[edit: formatting list]