Howard's screen name on the video game he was playing is "Fr00tL00ps511", alluding to the unfortunate nickname he was given when he was in space.
In one scene, Leonard mentions inviting Sheldon to see Fantastic Beasts: The Crimes of Grindelwald (2018). The episode aired the day before the film was released into theaters.
The Vanity Card at the end shows a picture of the cast together with Stan Lee, who guest starred in The Excelsior Acquisition (2010), and died three days before the episode was broadcast.
This is the penultimate time that Soft Kitty is referenced on the show. Due to a lawsuit by the descendants of the song's original composer in December 2015, it has rarely been heard in the show since the 8th season.
When the guys have a hard time imagining that anyone would be attracted to Sheldon, they are obviously forgetting Dr. Nowitzki (Riki Lindhome), Sheldon's admirer from The Cooper-Nowitzki Theorem (2008) and The Long Distance Dissonance (2017).