This app was mentioned in 2 comments, with an average of 1.00 upvote
as you mentioned doing RPG first, I think it's too complex anyway, and it's not something I would start with.
What I want to do is more similar to: https://play.google.com/store/apps/details?id=com.tradegame.airtycoononline2 or https://play.google.com/store/apps/details?id=com.soccermanagerltd.worlds or even https://ogame.gameforge.com/ if you think in terms of web dev.
My thinking is that all logic should be based on the server, and mobile app will be only visual layer, responsible for sending json request after clicking a button or update a state with some socket (ex. turn finished).
AirTycoon Online 2
https://play.google.com/store/apps/details?id=com.tradegame.airtycoononline2