I wasn't sure if I should report this as a bug or not. With a modal window, you can tab beyond the modal window into the URL, and then continue on into the page behind the modal window itself. I was able to recreate this on the Modal demo, and fire a search, even though I couldn't click to get there. As I saw in another post that it is essentially a viewport modal (https://feedback.telerik.com/blazor/1510450-prevent-the-user-from-dragging-a-window-out-of-the-viewport), would it be possible to force modal to be system modal, as was available back in the ancient Winforms days?
That's how a web page behaves. Code in a web page cannot and should not prevent the user from using their OS. The browser chrome (address bar, buttons and so on) are part of the OS, and as such are beyond the sandbox of the web app. The web app is limited to the viewport, it cannot go out of it, or interact or control elements outside of it. Anything else would be a severe security issue.
A system-wide modal dialog is only possible though a native application, but not in a web application.