Hi,
I think I found how to resolve this issue. I've updated my Macbook Pro 16" today to Big Sur and I had the same issue. Xcodebuild forced me to force reset my computer.
I have checked my xcode command tools path with xcode-select -p and I found that the path was related to an older version of xcode (10.1 in my case).
I have reinstall xcode command tools (sudo rm -rf /Library/Developer/CommandLineTools and xcode-select --install) and I have switch the xcode-select path with this command sudo xcode-select -switch /Library/Developer/CommandLineTools
My issue is now resolved