Just came across your post from a foray into much better content so thank you for that!!
I’ve found that going to busy.org and logging in with your Steemit credentials - you can go to your “Activity” tab to see interactions. I can’t figure out notifications either and even have the app installed.
Steemit is promising, but I’m also exploring other options. Not being notified of people responding to you seems like a problem even social media platforms 7 years ago would have thought to solve.