Those who need to keep MacOS-capable hardware around for development or maintenance purposes, or simply as a form of conserving resources may be interested to know how Apple is increasing MacOS requirements over time. In general, if the Apple computer is too old for a currently supported MacOS version, consider installing Linux, which normally works well on Apple computer hardware. Apple maintains a list of no longer supported Apple hardware.
The red dotted line depicts the oldest supported version of MacOS.
Data source is Wikipedia.