"Critical CSS is a must-have for a good pagespeed and core web vitals score". I saw this statement passing by recently, and although using critical CSS myself, such claim comes with nuance.
Last Thursday, January 16th, I joined TJ Gamble's livestream to answer some PageSpeed related questions. Critical CSS was one of the subjects. Just before the livestream, I published a code snippet to auto-enable CSS critical Path within Magento 1.
As of version 2.3.3, Magento introduced CSS critical path. Users will experience a faster loading product-page when applied (correctly)!