I have come across many You tube items that will not work in IE11 on Windows 10 and on Windows 8.1. I have looked at the manage add-ons and Name Shockwave Flash Object Publisher Microsoft Windows Third Party Application Component
Status Enabled Architecture 32-bit and 64-bit
This is in the list all addons, but not in the currently loaded addons.
The same you tube will work in Firefox or in Edge, but fro clients that require ie11 cannot view the you tube presentations. the error is because of flash not being installed, but when I try install flash, I get a message it is already built into windows 10