https://arstechnica.com/tech-policy/2020/11/as-trump-falsely-claims-victory-twitter-and-facebook-counter-misinformation/

As President Trump falsely claimed that he has won re-election despite the fact that votes are still being counted, Twitter and Facebook took steps to counter Trump's attempts to spread misinformation.

"Once President Trump began making premature claims of victory, we started running notifications on Facebook and Instagram that votes are still being counted and a winner is not projected," Facebook said. "We're also automatically applying labels to both candidates' posts with this information."