Honestly, apps from F-Droid are probably gonna work better on the Classic Flip.
All of these apps are Open Source so it would be easy for someone more knowledgeable than me to add cursors and fix the keypad input. I use a LOT of apps from F-Droid!
Element (formerly Riot.im) (Untested on Classic Flip as of this post)
Fennec browser (Unnecessary, there's already a good browser on Classic Flip!)
NewPipe (Can't access search on latest official, but a version I found on AptoideTV and signed works)
And a whole lot more apps I haven't listed yet!
What are your thoughts on F-Droid? Could this be a good solution?