No version earlier than 12 works on Big Sur.  Apple depreciated the API's that Fusion used, and it now leverages the built-in hypervisor framework.

Virtualization software has far deeper integration with the OS than almost any other application.  That requires significant development resources to be invested every time apple releases a new OS version, some more than others - and Big Sur was a big one.  VMWare isn't a charity, and that work has to be funded.  11.5 was a free upgrade from 11 for Catalina compatibility BTW - 11 was the last paid upgrade (for Mojave two years ago).