Brendan: The infamous "Berlin draw"...it's been plaguing chess tournaments the past few years, and Nakamura (along with Wesley So) is one of the most frequent practitioners.
Nakamura said in his daily recap
https://www.youtube.com/watch?v=-blkH58zFBk&t=525s
that he was surprised Rapport went for this, and that he expected Rapport to try to win. OTOH, by playing the Berlin Naka made it possible for the insta-draw to appear.
That game was the first of the second day. I looked up the results after day 1, see
https://chess24.com/en/read/news/world-blitz-day-1-magnus-cuts-it-close-hikaru-hunts-1st-title
Nakamura was in the lead on 10 points, Rapport was one of a group of 5 tied for second on 9.
The Berlin is notoriously difficult to beat with White (ask Garry Kimovich for instance 🤣; it may have cost him his crown). My best guess is that Rapport wanted to allow the Berlin; when it appeared on the board he figured he wouldn't be able to win, and decided to draw quickly and save energy for future rounds, maintaining his 1-point deficit to the leader. Meanwhile, Nakamura could maintain his lead, and drawing with Black vs. the formidable Rapport was an OK result for him.
On balance, I can understand the decision from both sides, but consider that Rapport chickened out to some extent. It looks like he's mostly a 1. d4 / 1. Nf3 player, see
https://www.chessgames.com/perl/explorer?pid=123427&side=white ,
and was perhaps hoping for the "Berlin draw".