On September 18, the results of an NPR/PBS/Marist presidential poll were released. This is one of the national polls recognized by the Presidential Debates Commission, and is the first such poll to ask about four candidates. See it here. -scroll down to page 74.
The results: Joe Biden 49%; Donald Trump 41%; Jo Jorgensen 5%; Howie Hawkins 2%; other 1%; undecided 2%. Thanks to Dalton for the link.