I went with Flask (python) + Bootstrap for my website.
The apps are created in Flutter, which was a great choice looking back on it. This allows me to have 1 codebase for both Android & iOS apps (most customers want both). If developing an app for just Android would be 100% effort, developing an app for Android and iOS with Flutter is around 130% effort I'd say. Those additional 30% mostly come from inconsistencies in Flutter between Android & iOS and from desired differences between the platforms, e.g. Material vs Cupertino design.
I developed native Android apps before and now I'd even use Flutter if I wanted to just create an ordinary Android app. It's just so much nicer to use in my opinion.
Summary: Flutter was a great choice, Flask is fine too, nothing to complain about there.