You should be able to embed it in the Community by clicking Share in Sharepoint, then Embed, and copy the embed code. Next, go to the Community post, choose HTML in the Editor tool, then paste the embed code.
Here's a public article where we embed videos from Vimeo using the embed code: https://help.powerschool.com/t5/Getting-Started/Getting-Started-Guide-for-Schoology-Learning-Custome...
We also use iframes on category pages by using a custom page that is blank and adding the iframe in the custom content in Admin. This is good if I want the items on the external site to be updated in Community without having to manually add it. Here's an example: https://help.powerschool.com/t5/Customer-Stories/ct-p/PowerSchool_Customer_Stories
Does this answer your question? Please let me know if I misunderstood.
