As much as Apple tries to prevent it with beta updates, to be tested by thousands of Apple developers for possible bugs, every now and then one of those "sneaks"bugs» in new versions of operating systems.
And it seems that one of those bugs is bothering some users of older Macs who use macOS Big South, and that their computers are incompatible with the current macOS Monterey. Well, if it is already a nuisance for them not to be able to update them, it is even more so when they are incomprehensibly receiving notices on the screen of their computers asking them to update to macOS Monterey...
When we upgraded our Macs a few months ago from macOS Big Sur to macOS Monterey, we noticed many new features (and those to come, such as Universal Control) that Apple incorporated into its new version of macOS. But for the full experience, relatively modern hardware is required, so the company excluded older Macs from the list of devices compatible with macOS Monterey.
So far everything is normal. It is normal that every year that passes and Apple launches a new operating system, whether for Macs, iPhones, iPads and other devices, older models "fall" from the list of compatible devices. And although Apple tends to "stretch" the age of such compatible devices a lot, it is the law of life.
But the curious thing about the case is that an error has appeared in the latest update of macOS Big Sur. Said "bug" causes on the screen of your old Mac from time to time a warning appears reminding you to update your computer to macOS Monterey, even though it's not on the list of compatible devices, and therefore can't be updated.
If you are one of the affected users, don't worry. Ignore the warning, and wait for Apple to correct it in a future update of macOS Big Sur. Now you have one more “excuse” to buy a new Mac….