Then you clearly missed out all the drama concerning image retention with the very first Mac that came with a retina display. That was back in 2012, iMacs only get a retina display in q4of 2014 about 2,5 years later
There are even people complaining about this very same issue on their iPhones.
Clearly this is not an iMac issue, it's a very generic one. The difference is in workloads and how good you are at spotting them. It happens in companies a lot where a lot of people are only working in 1 application and on displays used for presentations. Quality differences in TFT panels (even within batches) are a reason why one panel is more prone to this than the another even within the same batch. In some cases you can even clearly tell if the company has a "always lock your computer" policy by looking at the display. Usually the lock screen is burned into the panel. Rather funny to see
Clearly this is not an iMac issue, it's a very generic one. The difference is in workloads and how good you are at spotting them. It happens in companies a lot where a lot of people are only working in 1 application and on displays used for presentations. Quality differences in TFT panels (even within batches) are a reason why one panel is more prone to this than the another even within the same batch. In some cases you can even clearly tell if the company has a "always lock your computer" policy by looking at the display. Usually the lock screen is burned into the panel. Rather funny to see