Pretty easy, yes. Choose full screen from the view menu is usually what does it.
However, the app does have to support full screen mode, then that is not likely to happen, at least for
that app.
And, you would only have the option to zoom (maximize) to fill the screen. That is not the same, of course.
Which app do you need to support full screen? Not all apps are suitable for full-screen mode.
You could always ask the developer to see if that is a possible feature to add.
Sometimes you may get a response from the developer, maybe with an explanation about why full-screen is not supported, or you might discover it is not really "easy enough" to just patch it in.