I'd pick 'Follow system settings' - users often have a strong preference for syncing with their OS settings, and it reduces duplication of effort for them to set it in one place.

I'd pick 'Follow system settings' - users often have a preferred mode set for their device, might as well respect that choice.

I'd pick 'Follow system settings' - users often have a preferred setting and forcing one might annoy them.

I'd pick 'Follow system settings' as it respects user preferences, but have you considered accessibility implications for users with visual impairments?

I'd pick 'Follow system settings' as it allows users to stick with their personal preference, but have you considered user time-of-day habits?

I'd pick 'Follow system settings' - users often have a preferred mode set for their device, and mirroring that can improve overall experience.

I'd pick 'Follow system settings' - users often appreciate not having to manually switch modes, and it feels more integrated with their device's overall experience.