you could have just googled it but not every website is automatically PWA
you have to add a serviceworker.js which can be like a thing sitting between the app and the webserver, enabling one to make offline features aswell as a manifest.json, where you list app icons in different sizes vor android, iOS etc...
and that's pretty much it.
any site can be a PWA but in the case of bernd.group, it doesn't really make any sense because there are no extra features.
check out twitter if you want to get a good PWA experience