macOS root password & malware? I entered my macOS admin details (root password) into an application I think was malicious. Suspicious, I checked the keychain and my tokens had modified passwords.

What else could have this software done? Where would I look? More importantly what can I do to check / protect myself?

I deleted all keychain entries and changed all passwords...
You can get and run Malwarebytes. This supposedly finds any malware on your Mac. If that finds nothing I'd look for a virus checker with a free trial period and run it as a secondary test. Here is a link to a review of Mac virus checkers. Malwarebytes can be found at this link.