During Gamescom 2019, Geoff Keighley and Infinity Ward said that Call of Duty: Modern Warfare is getting an Open Alpha. It was said to be available on Friday (August 23, 2019). But it seems that Infinity Ward, and PlayStation let the cat out of the bag very early (as of this writing its 5:47 PST/7:47 EST on Thursday, August 22). You can download the new Open Alpha as we speak. All you need to do is go to the PlayStation Store, and look for the Featured area of PlayStation Store. Look for the “What’s Hot” section, and it should be the first thing you see.
You do not need a Call of Duty: Modern Warfare pre-order or a PlayStation Plus account to get access to the Open Alpha. You may want to download the Alpha as soon as you get the chance to do so – the download size is 35GB.