I also experienced same after upgrading to Sequoia 15.3.1 and found clang++ stopped working. It started throwing error "fatal error: 'iostream' file not found". As as fix, I had to remove CommandLineTool: sudo rm -rf /Library/Developer/CommandLineTools/ and reinstall xcode by: xcode-select --install This command threw an installation popup and took a few minutes to complete the installation. After successful installation, I checked CommondLineTool by: ls -l /Library/Developer/CommandLineTools , that showed: drwxr-xr-x 5 root wheel 160 Nov 17 2023 Library drwxr-xr-x 10 root wheel 320 Feb 24 00:33 SDKs drwxr-xr-x 7 root wheel 224 Jan 15 2024 usr It solved the defect and clang++ started working for me.