Thanks for your answers! I don't think I have follow-up questions to these points directly, but I started to watch BTCSessions' Passport video for batch 2 and he quickly said that you can 'decide what you get notifications for'.
There is a selection of 'All', 'Transactions', 'Updates' and 'Security'.

Does this mean the application has some kind of remote notifications built-in (that to the best of my knowledge need to go through Google and / or Apple servers)? Or is it just a 'notification page' inside the app?
And do you use Firebase or any other Analytics / similar type framework?