According to fantasy author Brandon Sanderson, a likable protagonist has at least two of the following attributes.
There are two ways to make a character sympathetic. One way is to make the character kind. The other way is to make the character suffer. John Wick starts out sympathetic because he loves his wife. John Wick becomes more sympathetic when his wife dies. John Wick becomes even more sympathetic when he is shown caring for his dog. John Wick becomes extremely sympathetic mobsters kill his dog and steal his car. John Wick is so sympathetic we're okay with him murdering 77 people.
We like reading about superpowered aristocrats who speak sixteen languages, hack computers, seduce hotties and can kill a man with a pencil.
Harry James Potter-Evans-Verres doesn't wait for Voldemort to make the first move. He hunts his nemesis proactively.
The characteristics of a likable protagonist are the characteristics of likable people in general. I preferentially befriend kind capable proactive underdogs. If you want people to like you then be kind, become capable and proactively pursue great ambitions.