I think part of the issue is that many people who post these questions are either converts from some other faith, which may have been one of those Protestant sects that stress “No Sunday Work” based on their interpretation of Scripture, or else they did not grow up in a very religious home, even if it was Catholic, and they are genuinely seeking what the “rule” is.
Also if you lived your whole life in a country where there were Sunday laws that closed all the businesses, and now those aren’t in force any more, along with other sweeping changes that are sometimes really contrary to Church teaching, it can be hard for folks to know what they need to do.
Fr. Altman has made a huge deal out of “don’t work on Sunday and if you do you’re committing the sin of avarice”, which is one priest’s opinion. Other priests would give other opinions. Often there is a cultural overtone to what’s considered unnecessary vs. necessary work. I can see where people get confused.
As a practical matter, I spent a few years living in a state that had “blue laws” that closed almost all businesses on Sundays well into the late 1980s, at which point the laws were repealed although some businesses still chose to observe them (especially businesses run by sola scriptura Protestants). It was often a lot of hassle dealing with the Sunday closures, as one would be working at an office job during most business hours all week long and then have to cram all necessary shopping and errands into a Saturday which didn’t make that day a very good “day off”, or the alternative was that you spent Saturday doing whatever you had planned for a “day off” and then went into the new week on Monday with a bunch of unfinished shopping and errands that you couldn’t do on Sunday. It was more work trying to plan around the Sunday closure than it would have been just doing the errand after Mass. We were all quite thankful to get rid of those laws. I was a regular Massgoer then and we had a priest who was older, had a PhD and was very holy and orthodox in his views, and he never said anything about Sunday blue laws.