Hey Xuri04,
You can use True Tone with these devices: iPhone 8 and later, iPhone SE (2nd generation) and later, iPad (9th generation), iPad Pro 12.9-inch (2nd generation) and later, iPad Pro 11-inch, iPad Pro 10.5-inch, iPad Pro 9.7-inch, iPad Air (3rd generation) and later, and iPad mini (5th generation) and later.
However, you should be seeing auto-brightness as a setting. Since you don't, we'd like to refer you to Apple Support. They will have the necessary tools to investigate into this matter more with you: Get Support.
Have a great day.