Good drills to practice for shadow stroke/footwork practice:
All of the drills in that video represent the fundamental footwork drills. Those are the ones to start with. Doing shadow versions of any/all of them makes sense. Start small. Once step first. When the coordination for the one step starts feeling solid, that is, when you have the independence/coordination of upper and lower body while doing the stroke with the one step, then it is time to add on. If upper and lower body are not sufficiently coordinated more than a one step will slow your progression.
When you can do all the exercises in the video as shadow stroke/footwork exercises, then it is time to try it with a real person feeding you the balls, or a robot. But since, this may be for something to do under shelter in place type restrictions, start with the shadow versions of the drills.
One nice thing is, the person doing most of the demonstration in the video is Zoran Primorac so you know the technique is stellar.
Learning from a good model for technique is worthwhile.
There used to be a video with Petr Korbel where they showed close ups of his feet during footwork drills where you got to see the subtleties of how he used his feet during the stroke and it was really helpful. Unfortunately, that footage got taken down. But, you can still watch closely how Primorac uses his feet here. It is illuminating for those who have the tendency of keeping the heels down. In this video you can see the places where Primorac digs his whole foot into the ground for power on the stroke or moving, and how much of the rest of the time his heals are lifted and you can see shadow under his heels.