This currently happening in both my application, and in some of your demos.  If you set the focus to one of the tabs in the tabstrip, and then hit the tab key on the keyboard, it should set focus to the tabstrip content itself.  However, in some cases it sets the focus right back to the tab, so you can never navigate off of the tab with the keyboard.  

An example of this can be seen in the Overview and Scrollable Tabs demos, but it is working in position and alignment demo.  I should also note that if I open the Overview and Scrollable demos in the Repl, it also works.  So I'm not sure what is preventing it on the demo pages themselves.  Any help would be appreciated, since the same thing is happening in my projects after I upgraded the Telerik controls to v9.x.  Here are the demo links that I'm referring to.

https://demos.telerik.com/blazor-ui/tabstrip/overview

https://demos.telerik.com/blazor-ui/tabstrip/scrollable-tabs