Cmd+Option+Esc not working in macOS Mojave 10.14.5
This is same as the shortcut you're trying. Apple logo in the menu bar in top left corner-> Force Quit. This should be done from an app whose menu bar is not in the hang(spin-ball) state. To achieve this, I normally click on desktop to get Finder.
A different approach, type Activity Monitor.app in spotlight(cmd+space) or via launchpad or via Applications folder. As your question seems like you're not talking about any application, the first method is not so useful.