Which would be a shame given how well Parallel works on Catalina. At least that is going to be usable for more than 12 months and will support more than a single major release of macOS. If v15 is not going to work on Big Sur I am definitely going to abandon Parallels again and purchase a VMware Fusion Pro license. I have just recently purchased a license and am definitely not interested in a) a yearly software subscription, or b) yearly mandatory paid upgrades because they refuse to support their software for more than 12 months or more than one major macOS release. Requirements for VMware Fusion 12: A Mac computer manufactured in 2011 or later (except 2012 Mac Pro Quad Core with the Intel Xeon W3565 Processor) 2010 Mac Pro Six Core, Eight Core, and Twelve Core with a graphics card that supports Metal. I really hope that Parallels is going to continue supporting v15 on Big Sur. Microsoft has a fairly extensive algorithm to determine when a re-activation is required. It probably depends on the amount and extent of virtual hardware changes.

However, when I first migrated a Windows 10 VM von VirtualBox to Parallels on my iMac it did. I migrated two VMs from VirtualBox to Fusion (1x Windows 7, 1x Windows 10) on my MacBook, which did not trigger Activation.

Vmware fusion 12 player