I know someone who was raised by their stepfather and biological mother for many years. Now that the stepfather divorced her mother, can he see her without a hijab on? Can they have physical contact? Should they not talk to eachother at all, since he can`t be a mahram for her?

All praise are due Allah. May His peace and blessings be upon His last and best prophet Muhammad.
Her stepfather has the same status of her biological father in this issue. Even after divorcing her mother, he is still like her father, and a permanent Mahram (immarriagable man) for her.

Allah knows best.