How can I support bootcamp assistant on this Mac

You can use BootCamp on Big Sur if you are using any of the older Intel-CPU based Macs:

https://support.apple.com/en-us/guide/bootcamp-assistant/bcmp173b3bf2/mac

You simply need to have the Windows 10 ISO image from Microsoft and follow the above instructions.

However, if you have one of the new M1-based Macs that recently came out, that does not support Boot Camp. You can consider downloading the trial of the latest Parallels software and run the technical preview for Windows 10 ARM version to run Windows.

From Install Windows 10 on your Mac with Boot Camp Assistant - Apple Support, Boot Camp requires a Mac with an Intel processor.