Apple - Upgrade to Big Sur Beta 3 Broke Brew Build system

Same thing happened to me, you need to install the most recent Beta version of command line tools as well as the matching XCode 12 Beta. The same thing also happens with git and other things added by the download https://developer.apple.com/download/more/?=xcode

Yep, was broken till I installed Xcode 12.2 Beta 3 / Xcode 12.2 Command line tools Beta 3. Not surprised, this happens every year. I've just received a notification that Xcode Beta 2 Command Line Tools will be automatically installed tonight but I already only have Beta 3 installed. It's a BETA and it's buggy.

Also, Homebrew's response:

$ brew doctor

Warning: You are using macOS 11.0. We do not provide support for this pre-release version. You will encounter build failures with some formulae. Please create pull requests instead of asking for help on Homebrew's Gihub, Discourse, Twitter or IRC. You are responsible for resolving any issues you experience while you are running this pre-release version.

I fixed it by doing: sudo xcode-select --switch /Applications/Xcode-beta.app.