I set time limits, but no I don't see any addictive behavior. If they ever start acting like that it gets shut down hard and fast, and I make clear playing Minecraft is a privilege. I never play with them, but I often ask them to show me what they built. They play on local worlds, or sometimes with each other, but not on public servers or with friends.
"She can earn her phone or computer when she publishes an app on the App Store."
I don't understand how building a piece of software that Apple is willing to publish on the App Store makes your daughter emotionally prepared for social media.
I don't have any problem with gatekeeping minors' access to social media (although I would be much more liberal in this area than you) but this metric seems absolutely bonkers to me. My heuristic from my own personal development would be that the earlier I was able to make some commercially viable software the later you should push my access to social media... my coding ability was never an indicator of my defenses against the common ills of social media for kids as I understand them!
You are misreading intent. When she is able to productively use computers as computational tools, she can have one. There has to be a positive to balance the negative.
That's interesting because if you set that out as a goal.. then what, right? What you'd like is on-going productive use once unlimited access is granted if your goal is balance. My inclination would be to be giving "homework" all the time, so the hours get split up somehow and aren't just spent of frivolous things once the privileges are acquired.
She uses my computer under my supervision (and tutelage--we're working through a few Swift tutorials right now). She doesn't have her own computer, or unrestricted computer time, outside of her school where they have Chromebooks.