It is now possible to send a push notification to a specific user on Bubble via Nativator.
Nativator.io appends the playerid to the converted app url, from which you can extract and save during sign up (or login). Parameter must be: playerid (text) - Make sure your signup pop is on the same page (submitted url to Nativator).
Once saved in your database, use any onesignal plugin offering ´send by device ´ option to automate your push notifications. Ideal for reminders, social media, chat app, delivery app etc
Note that you will need to configure your own Onesignal account and setup android and iOS platforms based on a specific package id (or bundle id) first to generate the APP IDs which will be used during conversion.