Click here to read an article by ChromeUnboxed, from April 2023, called "Chrome wants to turn the web app install process into a Google Play Store-style experience" that sets out the direction being taken by Google.
Click here to read an article by wired from September 2021 that provides aa full explanation with illustrations.
Click here to read an article by freecodecamp from April 2021 that introduces a lot of terms and techniques.
Click here to read "How To Build Progressive Web Apps" by outsystems.com that highlights feature of their development methods as well as giving a lot of background to the creation of PWAs and their benefits.
Click here to read "All about Progressive Web Apps and Implementation in Drupal" by specbee.com that repeats some of the information in the above outsystems.com article but contains more technical details about Drupal.