Windows 11 can be installed on computers that do not qualify for the upgrade. The problems come in after the upgrade. Microsoft requires that a computer meets certain hardware, like at least an 8TH generation processor as well as other requirements to work properly. There are many people advertising that they can upgrade your windows 10 computer to windows 11. With some special software this is possible. In a way the statement is accurate, but they do not guarantee that these upgrades will not have problems down the road.
I do think that down at some point Microsoft will come up with something that will allow the upgrade to older computers. It will probably come at a cost and no one knows when and if this will happen. If you own a computer that came from the factory with windows 10 you may qualify for a legitimate upgrade from Microsoft. If you own a PC that was upgraded from windows 7 to windows 10 you will probably be out of luck.