@rc4053 ...
You are correct. There is no option to edit YouTube videos within the Canvas Studio interface. Even if the YouTube video is your own and you add the YouTube URL to Studio so that the video appears in your Studio library, you cannot edit the video. If the video is your own and is hosted on YouTube, you'd need to do editing either in YouTube or offline to shorten the clip. Or, you could upload the video file directly to Studio, and then you could do some simple editing to trim the video down to the portion you wanted. Similarly, if the YouTube video is *not* your own, and you add it to your Studio library, you cannot make edits to it (such as trimming it down).
Sorry I don't have better solutions for you, but I hope this helps to answer your question.