The Tenseigan is an evolved form of the Byakugan that has so far, appeared in a select few characters in Naruto. The first person to awaken the Tenseigan was Hamura Ōtsutsuki, Kaguya’s son.
After Hamura, Toneri Ōtsutsuki, a descendant of Kaguya Ōtsutsuki managed to awaken Tenseigan and obtained God-like powers.
So if the Tenseigan was so strong, why didn’t Kaguya have it?
She had the Byakugan, so why didn’t she awaken the Tenseigan?