Do you have difficulty reading? The post is very explicitly about fake busy-work that accomplishes nothing with the goal of *looking* busy, thus punishing workers who actually work quickly and efficiently, this is incredibly widely understood concept and it's bizarre that you seem unfamiliar with it
No, I just choose to read and think critically opposed to only accepting things at face value, especially those on the internet. I would recommend you to do the same.
The post is very explicitly about fake busy-work that accomplishes nothing with the goal of *looking* busy
No it is not, which is indicated by OP's belief that their duties exclusively resolve around having customers and that when the business has no customers, they should be able to relax or do nothing as they are exhausted from dealing with customers. Although I am confident that they may exist, it is an extremely rare occurrence that a coffee shop would hire employees separately for servicing customers and for cleaning, especially one that has ample downtime for their service employees. Seeing as OP mentioned this phenomenon happening at every job that they have ever worked at, it seems unlikely to be the case.
Furthermore, OP is complaining about cleaning at a coffee shop, which if you have ever worked at any food business, then you would know there is no employee in the world that can keep it 100% clean, 100% of the time. Reasonably clean? Sure, but what is reasonable v. not reasonable is at the discretion of the employer. When I was a dishwasher, this would happen quite a lot by my coworkers who would get into verbal arguments with our manager about having to a) manually scrub dishes/silverware or b) run dishes/silverware through the dishwasher multiple times due to them not being "clean enough". To most employees that have no accountability for the success or failure of a business, a lot of things will be "good enough", especially when given the option between relaxing or doing more. OP even alludes to this fact when saying "That's your business, not mine."
thus punishing workers who actually work quickly and efficiently
That's not what is happening here because if that were true, then they would be complaining about dealing with customers too, i.e. quickly and efficiently serving X amount of customers and then being asked to serve even more customers. In contrast, the post is entirely focused about having to clean when there are no customers. Furthermore, if it were true, then they would be in the wrong line of work or they should seek a raise because as OP alluded to, they are performing a labor contract that provides payment-by-time, i.e. hourly. If they want to be paid for their added speed and efficiency, then they should get a job that provides payment-by-result, such as those that pay commission (i.e. sales) or by project/gig (i.e. lawncare, home improvement, Uber, Doordash).
Getting upset because the other party of the contract is trying to maximize the value of the hours being paid with reasonable requests, i.e. cleaning for a coffee shop worker, is childish.
this is incredibly widely understood concept and it's bizarre that you seem unfamiliar with it
It may be widespread, but it is misleading. I deal with this similar phenomenon on a regular basis, where I have direct reports that I delegate work to with target ETAs and quite often they finish early.
Guess what they get in return? More work!
Why? Because there is always more work to be done and getting ahead now or even creating additional work (i.e. reviewing, annotating, enhancements, etc.) improves quality and mitigates risk.
Is it punishing them? No!
It gives me ample supporting evidence to recommend them for a higher raise or even for a promotion.
It can catch mistakes/errors; in the case of cleaning, it is reasonably common to "miss a spot" and re-cleaning something perceived to be clean can reduce those discrepancies.
In many cases, it can create buffers for future issues/challenges, i.e. getting ahead now to mitigate the risk of getting behind later. This is one of the reasons that restaurants generally have extensive cleaning procedures at the beginning and endings of business hours, so that less cleaning is required during busy hours.
Though just to reiterate, OP isn't complaining about just being given more work, they are complaining that they have to do work besides waiting for customers, see: "You pay me because I'm here at the coffee shop, waiting for customers. I'm not at my house."