Alternatively, in your browser (Mac - Safari, Firefox, Chrome; Windows - Internet Explorer, Firefox), click the "Download" button on the top right corner of playing video to download. 2. Next, click the "Downloaded" category on the left portion to open the downloaded YouTube videos list. Joined May 1, 2011 Messages 112 Reaction score 0 Points 16 Location Boston, MA Your Mac's Specs iMac High Sierra Mac OS 10.13.6 (For me, I recently had issues with both macOS High Sierra 10.13.5 and macOS High Sierra 10.13.6 with my iPhone running the iOS 12 developer beta 3.) In this case, you'll need to be running the latest beta version of macOS, which, for the iOS 12 betas , would be for the macOS Mojave 10.14 beta.