You can purchase a full Windows license later on.
HOW TO RUN EXE ON MAC BIG SUR INSTALL
When you install Parallels Desktop on your Mac, the software will automatically detect that you don’t have a copy of Windows installed and will ask if you want to download the OS from Microsoft.
You also get 10% better battery life when running a VM, and can set your virtual machines to automatically return disk space when they are shut down. It launches twice as fast as before, handles DirectX content at a 20% better speed and delivers 75% better “git status” when running Linux. The move away from kernel extensions in favor of native virtualization code has helped deliver useful performance improvements. “Parallels invested more than 25-man-years of engineer programming to take full advantage of the new macOS Big Sur architecture and revamped kernel extensions to deliver our best Windows-on-Mac performance ever for our Parallels Desktop 16 customers,” said Nick Dobrovolskiy, Parallels Senior Vice President of Engineering and Support in a statement.
As a result of the abandonment of such extensions on the Mac, the company had to dedicate a great deal of energy to replace them with native Mac virtualization code. One major change in Big Sur is the removal of support for third-party kernel extensions (kexts), which is what Parallels relied on for its emulation.