I'd pick 'Follow system settings' - users often have a preferred system-wide setting, and forcing an app mode might clash with that.

We tried setting our app to dark mode by default and got some pushback from users who said it made certain UI elements less discoverable; have you thought about A/B testing the two modes?

I'd pick 'Follow system settings' - users often have a preferred mode set for their whole device, so syncing with that seems intuitive. What about considering an override option for specific parts of your app?

We tried 'Dark mode by default' and got complaints about readability; consider A/B testing to inform your decision.

I'd pick 'Follow system settings' - users appreciate control over their experience. What about accessibility implications?