In the original story, Kaguya Otsutsuki's personality received little attention, but the Sage of Six Paths' account gave a rough idea of what she was like. (I'm going by the manga, not the anime, though some details overlap.)
After eating the God Tree Fruit, Kaguya Otsutsuki single-handedly ended every war in the world, and people came to call her the Rabbit Goddess.
It was no insult, but the highest praise they could give Kaguya Otsutsuki.
Yet as time passed, Kaguya Otsutsuki's personality changed drastically, as though she had lost her senses.
Gradually, Kaguya Otsutsuki came to believe that all Chakra belonged to her alone. She used the Rinne Sharingan to cast Infinite Tsukuyomi on the people, inspiring fear and awe. At some point, the honorific "Rabbit Goddess" gave way to "demon."
Her desire for Chakra eventually turned toward her own two children, Hagoromo Otsutsuki and Hamura Otsutsuki.
To reclaim all Chakra, Kaguya Otsutsuki merged with the God Tree and became the Ten-Tails, then fought her own children.
Of course, everyone knew how it ended: Hagoromo Otsutsuki and Hamura Otsutsuki used Six Paths: Chibaku Tensei to create the moon and seal Kaguya Otsutsuki and the Ten-Tails inside it.
In his previous life, people had often debated why Kaguya Otsutsuki's personality had changed so drastically, and whether it made any sense.
Then, after Boruto's Naruto movie came out, it was revealed that Kaguya Otsutsuki had an enemy in Ōtsutsuki Taoya.
The official explanation became that Kaguya Otsutsuki had used Infinite Tsukuyomi to create White Zetsu so she could resist enemies like Ōtsutsuki Taoya and Momoshiki Otsutsuki.
But could the White Zetsu Kaguya Otsutsuki created really fight someone like Momoshiki Otsutsuki?
Even Uchiha Yin had been unable to resist pointing out the absurdity.
Compared with Momoshiki Otsutsuki, the White Zetsu were pitifully weak.