Keyboard Replacement or Whole Top Case?

I have been offered super cheap a 2019 MB Air (Rose Gold)

ISSUES: • Needs reinstalling Mac OS; This is easy.... but then the description goes on to say, Some keyboard caps are defective; needs keyboard REPLACEMENT and CLEANING • Lag • Battery drain • A bit dirty overall; needs cleaning up.

There is no keyboard replacement guide only for the whole top case so just a KB swap isn't possible? and that would also lose the finger ID? Correct?

I am not savvy on these 2018 and up models for obvious reasons......