We have no experience with this OS.
Do you have any issue with starting Brainstorm on it?
Matlab 2020b officially supports MacOS 11.
The following page suggests that 2020a works as well, therefore the compiled version of Brainstorm should work:
https://fr.mathworks.com/matlabcentral/answers/641920-does-matlab-support-macos-11-big-sur
Try following the instructions from the installation page, including the details for MacOS:
https://neuroimage.usc.edu/brainstorm/Installation#Start_Brainstorm
If MacOS blocks the compiled version of Brainstorm with a security message, try to run it from a terminal, or as described in this article:
Please share you experience, it will help other users.
Thanks