If you want to start an app using a single keystroke, you can do so by creating an Automator Quick Action and giving it a shortcut in System Preferences . This is usually not necessary for apps that we have always run, but may be useful for apps we often download, and then end when not in use. You need to be careful not to use a name or shortcut that is in conflict with anyone else. You may also find that it is a bit flaky when you first create the shortcut.
Check out Create a Mac keyboard shortcut to launch any app on YouTube for closed captioning and more options.