The noun (Substantiv/Nomen) Stories is feminine in German. Therefore, the correct definite article in the nominative singular is die. So, you say: die Stories.
(stories)
Kurze, oft visuell ansprechende Inhalte, die auf Social-Media-Plattformen nach einer bestimmten Zeit automatisch verschwinden.
Short, often visually appealing content that disappears automatically on social media platforms after a certain time.
Ich poste oft Stories auf Instagram.
I often post stories on Instagram.