Dark mode

If, as your signature states, your iPhone is on iOS 12 software, then you need to update to use most recent software, iOS 14.6 at the moment.

Update your iPhone, iPad, or iPod touch

https://support.apple.com/en-us/HT204204

bimpe ~ How to turn on Dark Mode:

1. Go to Settings, then tap Display & Brightness.
2. Select Dark to turn on Dark Mode.

Use Dark Mode on your iPhone, iPad, or iPod touch

...found by searching Apple's Knowledge Base.

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bimpe65 wrote: "I am using the iOS 14.6 already i just updated it"

Just to confirm:

Settings > General > About > Software Version?

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