There is a known browser bug for any YouTube embedded video that tries to play in another site like Schoology when using a Chromium-based browser such as Microsoft Edge or Google Chrome. If you have this issue, please try opening the video in another browser, such as Firefox. Or you can embed the YouTube videos using a share link instead. To do that, please follow these instructions: SAU19 Knowledge Base - Kaltura - Adding a link to Media Directly Into Schoology.
Kaltura - Video in Course Will Not Play
When trying to open a video that is embedded in a Course, the video will not play. What do I do?