Every office has a different office culture, and that's to be expected. Some workplaces have people working constantly, including on the weekends. While that's not the worst thing in the world, it's weird to insist on people continually working overtime, especially without the proper overtime pay. It's even stranger to ask workers to work 8 hours on the weekend for something that isn't even in their job description. For instance, deep cleaning the entire office for the first time since at least March of 2020.
I am certainly not above cleaning. However, if my boss told me I had to come into work on a Sunday to deep clean the office and got paid in cash only, I would be highly suspicious. If you're a higher-up at a company that demands a lot of overtime, but be honest and pay the overtime instead of trying to get away with under-the-table foolishness. One man saw his girlfriend's job trying to rope her into this exact situation, and he was not happy about it.