Fix Homebrew (Brew) on macOS 11 Big Sur

If you encounter issues with brew on macOS 11 Big Sur, than it has a high chance of being a similar issue that I ran into.

One of the many error messages regarding brew on macOS 11:

Traceback (most recent call last):
 11: from /usr/local/Homebrew/Library/Homebrew/brew.rb:23:in `<main>'
 10: from /usr/local/Homebrew/Library/Homebrew/brew.rb:23:in `require_relative'
  9: from /usr/local/Homebrew/Library/Homebrew/global.rb:37:in `<top (required)>'
  8: from /usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.3/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
  7: from /usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.3/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
  6: from /usr/local/Homebrew/Library/Homebrew/os.rb:3:in `<top (required)>'
  5: from /usr/local/Homebrew/Library/Homebrew/os.rb:21:in `<module:OS>'
  4: from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:58:in `prerelease?'
  3: from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:24:in `version'
  2: from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:24:in `new'
  1: from /usr/local/Homebrew/Library/Homebrew/os/mac/version.rb:26:in `initialize'
/usr/local/Homebrew/Library/Homebrew/version.rb:368:in `initialize': Version value must be a string; got a NilClass () (TypeError)

How to fix this?

Remove old xcode command line tools

sudo rm -rf /Library/Developer/CommandLineTools

Install new xcode command line tools

sudo xcode-select --install

Update brew

brew upgrade

Note: I had to run it twice

If you still get an error message try to reinstall brew via:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Test if brew works

brew doctor

Now brew should work just fine under macOS Big Sur!