Since V5 the scoring has been changed as compared to V4. The documentation explains the score of Performance, Progressive Web App, Accessibility, Best Practices and, SEO but does not explain about overall score. As per the image it is 59 for Desktop.
Can Anyone help me regarding how the overall score is calculated?
I don't know how it is calculated but if you're looking for the total score in the new API v5, you will find it inside the json response in the following path lighthouseResult.categories.performance.score. I tested it over multiple websites and it works fine. Please note that score returned from the API deviates few points from the score displayed in the Page Speed online page
Reference answer Find score inside json result of PageSpeed Insight api v5
