У вашего броузера проблема в совместимости с HTML5
This is Part 6 of the OpenTK Platformer Tutorials Series. In this part we are going to look at how to make our own Input class which will allow us to check and handle keyboard and mouse input right from within the Update function.
The source code for the original stream is no longer available but you can download a working example at: http://www.siltutorials.com/blog/2017/1/3/opentk-platformer-source-code-kinda