Ever tried using Boot Camp to install and run Windows? It works only marginally. And it won’t install Linux. For that you need a UEFI boot manager Apple doesn’t support, and which works worse. The reason for all of this is simple. The new OS install still has to work with the firmware. Apple tries to bridge that gap for Windows to entice Windows users to try a Mac, confident they’ll ultimately prefer Mac OS. Supporting Linux would be a waste of their developer time.
Apple hardware and software are carefully optimized to work with each other. Buying a Mac to install another OS on it is a waste of money. If you want a Mac, use Mac OS. If you don’t want to use Mac OS, don’t buy a Mac.
