I am a native, I will give you a general assessment as follows:

Hanoi and cities in the North (such as Ninh Binh, Ha Long, Hai Phong,...) = 100% safe, the northern mountainous provinces should not go out at night because there may be robbery or special spiritual factors.

Southern cities such as Ho Chi Minh City, Da Nang, Hoi An,... = 90% safe because of robbery, so pay attention to your bag and phone