In Galatians 4, Paul says Hagar stands for which mountain?

Answer: Mount Sinai

Paul treats the two women as two covenants: Hagar stands for Mount Sinai in Arabia and corresponds to the present-day Jerusalem.

“These things serve as illustrations, for the women represent two covenants. One covenant is from Mount Sinai and bears children into slavery: This is Hagar. Now Hagar stands for Mount Sinai in Arabia and corresponds to the present-day Jerusalem, because she is in slavery with her children.”— Galatians 4:24-25 (BSB)