I think the fact that anyone could get fired for failing to show up to work for a protest is what makes it powerful. Like, you understand the risks and take them anyone. It’s obviously unfair that some businesses respond by closing that day (common where I live) but others fire their employees. I guess I just sort of assume anyone could get fired at any time for a variety of fair and unfair reasons so this isn’t shocking.
As to what’s worth losing your job over to protest that answer could change 1000 times between different protests that come up. Too many variables to make a stand.