Question

What’s the difference between a twin and doppelgänger

Answer 1

a twin is someone has has the same genes as you making you genetically alike and possibly facially, a dopplganger is a version of you who has opposite characteristics

Answer 2

Hello!

A twin is one of two children (or animals) that are born at the same time, and have the same mother.

A doppelganger is different. It is a person who looks just like another person, a lookalike. It's an apparition of another person.

These are the differences between the two.
A twin can also look like you, just like a doppelganger, but the doppelganger won't have the same mother and they most likely won't be born at the same time.