One of the only movies that remains intriguing throughout despite being basically a single conversation.

I happen to love certain niche movie genres, which happens to include "dinner party movies". Feel free to list some recommendations, if you like "people talk in a room" movies.

Some of my favories:

    Coherence (scifi)
    Garden Party (sleazy young adult Los Angeles drama)
    Murder Party (low budget horror comedy)
    How English sounds to non-English speakers (youtube)
    Circle 2015 (scifi)

12 Angry Men. My Dinner with Andre. Steve Jobs (a stretch, but much more a play than a movie).

There's some play adaptations which have few characters and mostly dialogue: Carnage, Who's Afraid of Virginia Woolf, Glengarry Glen Ross

Linklater's "Before" trilogy is also heavily dialogue-based, but the there are multiple locations.

"How About Adolf?" (2018) [0].

"Perfect Strangers" (2017) [1].

[0] https://www.imdb.com/title/tt7477310/

[1] https://www.imdb.com/title/tt6101820/

El método (2005) is a really good take on corporate/personal dynamics.

https://www.imdb.com/title/tt0427582/

The Big Kahuna (1999) ("the majority of the film takes place in a single hotel room, and nearly every single line of dialogue is spoken by one of the three actors.")

Not exactly a dinner party movie, but Sleuth (1972 and also the 2007 remake) is a good one.

I love those kinds of movies. It's a Disaster (2012) is a good watch.

Exam (2009) is another good single-room film.

The Invitation (2015 film)

What about "My Dinner with Andre?" That's exactly a single conversation.

And so is, mostly, "Rope."

Just don't look up the sequel.