If you are sharing video on Google Chrome or another browser but your viewers just see a black screen, it is most likely because your hardware graphics acceleration is not disabled in the settings. See below for instructions to change this. Note: this may be a setting to toggle off when necessary but otherwise leave alone as it has some effect on Chrome's memory usage.
Simple instructions for Chrome:
Go here: chrome://settings/?search=hardware
Click: Use hardware acceleration when available to turn it off (the dot is blue when it's on, gray when it's off)
Click the relaunch button to relaunch Chrome with the new setting
For best results, also use the "Optimize Share for Full-screen Video Clip" setting in Zoom. You can find this setting in the "... More" menu at the top of the screen when screen sharing is on.
More details available on Kast website.