MacworldI recently wrote about the M4 Macs compelling lineup and its a great time to buy a Mac. However, one type of user will want to hold off on a purchase. According to Howard Oakley of The Eclectic Light Company, the new M4 Macs will not allow virtual machine software to run properly. Users who want to run macOS versions older than Ventura 13.4 through virtualization will find that the virtual machine will not boot and users end up with a blank screen. Since the virtual machine (VM) wont boot at all, theres no way to access the log to see what could be the problem.Oakley reports that Activity Monitor shows that with the VM, only one CPU core is active even though multiple cores are allocated. This could mean that the issue happens before the VM kernel boots the other cores, an event that occurs early during the kernel boot phase. Until that point, pre-boot phases and the kernel run on just a single CPU core.This limitation means that VMs on M4 Macs can only run macOS Ventura 13.4 and later. The issue doesnt affect M1, M2, and M3 Macs, which can run VMs with macOS Monterey 12 or later. M-series Macs cannot run VMs of macOS Big Sur 11 or earlier. Oakley has tried running the VM on a single CPU core, but it still did not work on the M4.The issue has been reported to Apple but its unclear if a fix can or will be made available. Oakley suggests that Apple could fix the issue by modifying the kernels of the older versions of macOS, but that seems like a task Apple isnt going to do. So for now, if running older versions of macOS is vital to your workflow, you might want to hold off on a new M4 purchaseor at least keep an older Mac around.