If you want to know how to put Friday Night Funking in Full Screen, then you have to see this.
Check this tutorial to put Friday Night Funkin in full screen
Remember that to play this way you need a good internet connection and meet the minimum requirements to play this game without much freezing.
Another way that we recommend is the web pages that have the game for free. Play online, for free, but yes, you must have good internet.
Finally, download the FNF optimizer, which you can get by searching in your favorite search engine.