Calling it a one-shot movie focuses on the filmmaking, the craft involved in making the movie look the way it does.
While the filmmaking craft is certainly worthy of note, and will hopefully be well rewarded at the Oscars, the story is what engages the audience and everything, including the great cinematography and editing skill, is in service of that.
Certainly, referring to 1917 as a movie with no cuts, rather than a one-shot movie, is a nuanced position, but it also makes some sense.
Referring to it as a movie without cuts focuses more on the story, the fact that we won’t be leaving these characters for even a moment.