The Mudita Kompakt is a minimalist phone so it doesn’t do notifications like a normal phone would. So no you don’t get the badge on the app icon and you don’t get notifications on the lockscreen etc. But when you have ringer on, you’ll here notification dings whenever you get an iMessage text.
One work around is I have switched to using the inkOS launcher and now when I get an openbubbles message, there is a little asterisk and you can even have it give you a little text preview of the message on your homepage. inkOS v0.4 update