Hey there j0keeeeer,
Thanks for reaching out to the Apple Support Communities. To get started, when you say that True Tone is missing, are you not seeing the setting in Settings > Display & Brightness, or is True Tone not adjusting the display color and intensity as expected?
If you're able to see the setting but True Tone is not working as expected, try turning True Tone off, restart your iPhone, and turn True Tone back on.
Restart your iPhone - Apple Support
How to restart your iPhone 6, 7, 8, or SE (2nd or 3rd generation)
1. Press and hold the side button until the power-off slider appears.
2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button until you see the Apple logo.
Let us know if that's able to help.
Take care!