Parallels fixed the crash I reported almost immediately. Since then Parallels Desktop 16 has always worked well; it worked fine in macOS Catalina and works great, like a bolt of lightning , now that I have Big Sur installed, although my 27 '' (late 2013) iMac is not supported and I had to use Micropatcher to install. An important tip: if you have a Fusion Drive try to transform it into an SSD as soon as possible. After eliminating Fusion Drive, so, replacing the internal mechanical HD with a great 2TB SSD, I used Apple's original internal SSD, 128GB, to place the Windows 10 Pro VM. YOU HAVE NO IDEA how Winzozz now start-up immediately and runs fastly!!! Before, instead, with the Fusion Drive, loading was very heavy since Fusion Drive must first transfer the VM to the 128 GB SSD. If a Mac is nearly empty, the VM stays in the Fusion Drive SSD, but if you have a lot of data ... then the VM goes from Hard Disk to Solid State Disk and it's pains.