Taking portraits outdoors at night, the background light is very bright, but the characters are backlit. How to measure light and set aperture shutter to make people's faces and backgrounds clear?

This is also backlighting. Unless your camera has a large dynamic range, you can only fill the portrait with a flash.

To add:

1, the portrait mode at night is flash+slow shutter synchronization. If your background brightness is relatively high, you don't need this mode.

2, the night tripod mode is a slow shutter, of course, it is even more wrong.

3. Night hand-held mode is high ISO mode, so it is not used.

If your background can be exposed normally at a higher shutter speed, you only need to fill the portrait with a flash. Think of it as a normal backlight shooting.