Only GIF formats support loop properties natively. For other video formats, you can bake a finite number of loops into your project using Jitter and components.
Here's how:
Add your elements (layers, text, shapes, animations) to an artboard to compose your component. When you're happy with how it looks, select the artboard.
Click ❖ Create component in the property panel, or right click and select Create component. This makes your artboard a main component.
Copy and paste the component onto any other artboard. You can now edit the main component to update all instances.
With your animation packaged as a component, you copy as many instances as you need and arrange them back-to-back on the timeline.
When one instance finishes playing, the next begins, creating a continuous loop.
💡 Tip: Make sure your animation's final frame matches its first, so the transition between instances is invisible.