I am using also Mac hardware with Big Sur and to download charts and plates to the USB-Sticks, I run a virtual Windows session.
Seattle Avionics does not offer any Mac App to download the data, however they do have a Windows program that does the job.
This is how I run it:
* VM Fusion Player - Personal use license - free
* Windows 10 as virtual machine. Bought for $32 at kinguin.net
Cheers
Felix