PWA = progressive web app: it enables a browser to perform like an app without needing to install the app.
Yes you can log into multiple accounts with same app in diff profiles, however I wouldn't rely on this method to prevent the website from associating 2 accounts if the website uses device fingerprinting.
You only get push notifications for apps that rely on FCM (firebase cloud messaging) if you install Sanboxed Google Play in those profiles.
Apps like Signal and Tutanota can receive push notifications without Google Play installed because they will use their own push implementation if play services is not available.