This just seems like too little, too late. Much of the problems I see aren't advertising in the traditional sense, but viral content from sketchy sources. If they wanted to seriously affect this, they would prevent posts from spreading to tens of thousands/ millions of people without being vetted.
I think the possibility of election "chaos" is starting to look real; you've already had this year "armed protestors occupy State building", "crowdfunded anti-protestor gunman", huge ongoing demonstrations, voter rights lawsuits, and chaos in the mail system on which mail-in ballots depend. This is going to make the whole Bush vs Gore hanging chad debacle look like a gentlemanly dispute from a vanished age.
Those at the top of Facebook won't mind a clean victory for either side. They don't even mind a one-off clearing of the streets with live ammunition. What they will mind is ongoing violent struggle for the legitimacy of the state.
(absolutely not a given, but definitely a risk. Much like the President catching the virus that's dangerous to unfit people over 65.)