I have a MacBook Pro and I'm running Big Sur. I'd like to install either Yosemite or Sierra as a virtual machine. I downloaded the .dmg files but when I try to install them it says "unable to detect operating system." Customer support told me that I need to use an .app file, not a .dmg file. I tried searching for MacOS .app files but I can't find them. Does anyone know where to get them? Or is there a way I can use the .dmg file? Thanks.