I deleted the command tools directory given by xcode-select -p due to npm gyp error.
xcode-select failed to install the files with the not available error.
I ran the Xcode application and the command tools installed as part of the startup.
npm worked.
However this didn't fully fix the tools. I had to use xcode-select to switch the path to the Developer directory within the Xcode application directory.
sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
MacOS catalina.