Just copy the embed code from YouTube or other platforms, and paste it in the markdown file.

---
title: Include Video in the Post
published: 2023-10-19
// ...
---

<iframe width="100%" height="468" src="https://www.youtube.com/embed/5gIf0_xpFPI?si=N1WTorLKL0uwLsU_" title="YouTube video player" frameborder="0" allowfullscreen></iframe>