Once Upon a Snowman, on Disney+ (about 8 minutes)
Disney Animation; Disney Wiki; IMDb; On Disney+; TV Tropes; Wikia; Wikipedia
Note: I originally classified this as a "special", so that's where I have my entry for it. Since then I've come to think of it as more of a short film, but I don't feel like moving the entry.
There's not much to say about this without giving away the whole story. So, um... it debuted on Disney+ in October 2020. It shows the story of everything that happened to Olaf between being created by Elsa and meeting Anna and Kristoff. It's all rather amusing, and very... Olaf-y. I really liked it, and how it fits into the Frozen franchise. And I guess that's all there is to say.
feature films: Frozen * Frozen II
short films: Frozen Fever * Olaf's Frozen Adventure * Once Upon a Snowman * Myth
series: At Home with Olaf * Olaf Presents