This tweet has not been 100% verified by a reliable source. It could very well be someone just screwing around with the inspector in their browser and passing it off as authentic. Or Trump could have actually tweeted it. Just as likely. Trump was indeed active on Twitter at the time, his last one prior was at 6:41 PM EDT Wednesday.
UPDATE 8:43 AM EDT 10/22/20: The tweet is confirmed to be fake by Media Matters editor Parker Malloy. National Zero did hedge in the article content, but not the headline. We apologize for the lack of circumspection.