After downloading MacOS Mojave to install via Parallels Desktop 16 on my iMac running MacOS Big Sur, I proceeded to have Installation Assistant to find the disk image automatically. The assistant returned a message saying no disk image could be found. I then manually dragged the disk image on to the Installation Assistant window, where I received the error message "Unable to detect operating system." I then downloaded another copy of Mojave from another site, and received the same result. As I really need to get Mojave running virtually so that I can use a specific software for work that cannot operate in Big Sur, how should I proceed at this point?