The “cl.exe” error means you may not have Visual Studio C++ installed?
I’ll try and install the plugin here, and see what’s up
However, the plugin is optional, and you should be able to use standard SWFs with OpenFL, without a loss of features
EDIT: Oh, I just realized you are using Extension Manager. I don’t think that works for Animate anymore.
Visit https://exchange.adobe.com/addons and click to install the OpenFL Plugin from there. It should add it to your Creative Cloud account, and cause the Creative Cloud downloader to download and install the plugin for you. See if that works?