Ha! Sorry. Totally missed that...

-Dropbox has had API changes, so you are out of luck there.
-Instago was the only Instagram app for Harmattan (even though it was only a viewer), but that stopped working (for me) long ago.
-Last I checked Tweetian was still working well on my N9 (but, so was the native Twitter app).

Harmattan developer support leaves lot to be desired in 2018. If you want to continue to use your N9, mobile sites might be your only option for lots of services.