In case anyone else has this issue.
I was trying to enable Google oauth for an organisation so I can hopefully smoothly on board them to using The Bug Genie 4.2.1 on a project or two. I had installed The Bug Genie via Softaculous. Unfortunately, the module downloaded from the web site did not work as it's not compatible with 4.2.1.
To get it working I was able to download from https://gitlab.com/thebuggenie/module-oauth2-google
Extract the contents of this to a folder in
project root/modules named oauth2_google
composer install in that directory to install the supporting libraries.
From bug genie interface settings you can enable the module.
Then you can create an app in google, in addition to the advice on the module page you can go to https://developers.google.com/identity/sign-in/web/sign-in to help you generate what's needed.