I'm not sure why some think it's their constitutional right to go into someone else's store without a mask if the people that own the store/business require it, don't they have rights as well in their own store/business? Since the 60s I've seen signs in businesses that say "No shirt no shoes no service". No social or political outcry about that, but a mask?..."oh my gosh!... public health be damned, I want my constitutional right to not have to smell my own bad breath inside someone else's place of business."
You are correct, the Constitution has nothing to do with private stores and masks. Most people are irritated about the governments "ordering" it. The Federal government has zero standing on it, but States have a pretty good leeway with it, however. Although the extent is debatable. Interestingly, the Fed has not overstepped bounds at all during this crisis, not that I have seen. Some of the States have gone way too far, though.
Next they'll want their freedom of speech right to cry "fire" in a crowded theater.
Actually, you have that freedom. The controversial and incorrect non-binding decision in which the example was uttered (but not really related to the actual case) was overturned by the Supreme Court something like 50 years ago...
https://www.theatlantic.com/national/archive/2012/11/its-time-to-stop-using-the-fire-in-a-crowded-theater-quote/264449/There are some limits, but mostly civil, not criminal, and revolve around slander/liable and copyright. The few criminal exceptions include speech specifically (and intentionally) directed at a crowd or individual to incite [usually] immediate physical violence. Just saying something inflammatory, nasty, hateful, or controversial doesn't come even close to the standard.
Freedom of speech/expression/writing/protest is the best-protected of the Bill of Rights. I only wish the same vigor were applied to ALL of them, most especially the 2nd, 9th, and 10th. The 9th and 10th are gutted so badly, and so completely ignored, they might as well not even exist.