I'm gonna go ahead and predict that the #1 song of 2020 is "Blinding Lights" by The Weeknd. It has been in the top 10 since 3/21. If it wasn't for that long run, I'd pick Post Malone's "Circles", which had a lengthy top 10 run as well, including three separate stints at #1, not done on AT40 since Chic's "Le Freak" back in early 1979.
And you're right. "Blinding Lights" and "Circles" were #1 and #2 for 2020.
The 2020 year end countdown was marked by one major historic AT40 inaccuracy. Ryan stated that Dick Clark was the first ever AT40 guest host, when in fact it was Dave Hull, several months earlier. Dick Clark's intro into his 3/25/72 guest hosted show was played, and was followed by Ryan plugging "New Year's Rockin' Eve", which Clark started and Seacrest keeps up yearly. That led into an AT40 Rewind extra of Miley Cyrus' "Party In the USA".
That clip of Dick Clark features a mistake by Dick. He said that Isaac Hayes hit #1 in December with his single and album. Except that the "Theme from Shaft" and the soundtrack both hit the top in November (1971).