I have a few photo bursts in Photos.app version 5 (MacOS Catalina), and Photos.app identifies them as bursts, but I cannot find any tool in the interface to select one picture in the burst or even to view them all. I don't remember if the bursts were taken with my iPhone or with a Sony a6000, and surprisingly, it does not tell in the info of the photos.
Also, there is no
Make Selection... button when I open the photo burst that appears, as was suggested in an answer below, or as I have seen in some tutorials. I don't know if this is caused my something particular with my pictures or if Photos.app version 5 is different.