After upgrading MacOS to MacOS Big Sur, we will encounter an error: your CLT does not support MacOS 11.6. When installing or updating software with brew , we just need to reinstall Xcode select
solution:
enter the following command

sudo rm -rf /Library/Developer/CommandLineTools
sudo xcode-select --install 

At this time, you will be prompted to install Xcode select. In the pop-up box, we click Install, then the agreement will pop up, and then we click agree. Then wait for the installation to complete.