On the madewithlove blog Frederick Vanbrabant wrote a post on how he and colleague improved the PWA score of their company site.

So the first thing you should know about PWA (or progressive web apps) is that it’s an adaptation of your current site or web app. This means that if you want to have all the features of a progressive web app, you are going to need to change your current site/application. The good news here is that they are all changes you would want to have anyway.

https://blog.madewithlove.be/post/improved_pwa_score