E-E-A-T is more of a concept than a concrete metric for evaluating websites and individual pieces of content. The E-E-A-T score is a myth. There is no single summary E-E-A-T score. According to Google, there is no single E-E-A-T score into which all signals are aggregated or added up. I can imagine that Google gets an overall impression of E-E-A-T of an author, publisher or website through many different algorithms. This overall impression is not so much a score, but an approximation of sample image for an entity that has E-E-A-T. Google could use selected sample entities to train the algorithms to produce a benchmark pattern for E-E-A-T. The more the entity resembles this pattern image across different signals, the higher the quality. More on this in the related posts I mentioned earlier.