How do I duplicate videos so I can trim them (to make video clips)?

Reylin4  - The others are correct we don't have a way to do this today and it's not on the planned roadmap. But you should add your ideas / votes / comments in our ideas forum: https://aka.ms/StreamIdeas

Existing ideas to add to:

Copy video: https://techcommunity.microsoft.com/t5/microsoft-stream-ideas/copy-a-video-to-other-channels/idi-p/677434 (Thanks Tomislav Karafilov )

End video at time code - ability to make short clips from longer video: https://techcommunity.microsoft.com/t5/microsoft-stream-ideas/add-ability-to-end-video-at-time-code-way-to-make-short-clips/idi-p/110168