The movies are actually a two-part adaptation of the Sailor Moon Dream Arc, and is the first animated adaptation. Since the arc has never been animated prior to this, it also contains the first transformation sequence for Sailor Saturn.
Here’s the summary of the movie, as provided by Netflix:
Based on the ‘Dream Arc’ of the original hit manga series, the two-part movie is about the Sailor Guardians’ growth, both as teenage girls and as Sailor Guardians, as well as the faint first love of Chibi-Usa and Helios. As the new moon obscures the sun and gradually dims its light, Usagi and Chibi-Usa encounter a mysterious Pegasus named Helios, who is in search of the chosen Maiden who can break the seal of the Golden Crystal. Meanwhile, a mysterious troupe called the Dead Moon Circus appears in town, hatching a nefarious plan to scatter the nightmare incarnations known as Lemures, seize the Legendary Silver Crystal, rule over the moon and the earth, and eventually dominate the entire universe.
While Netflix announced they would be bringing both parts of Sailor Moon Eternal to the platform, they haven’t mentioned if this meant the arrival of Sailor Moon Crystal, the more manga-faithful adaptation of the Sailor Moon series that leads up to Eternal.