As the title says.
It won't lock unless the door is shut.
If the door is not shut, it goes down, like all the other door locks, but then very slowly slides back up.
Idk where to start on fixing this.

 

What you're describing sounds like the normal feature of the driver's door lock to minimize accidental lockouts.

To lock the driver’s door, pull the outside
door handle and push the lock tab
down. Release the handle, then close
the door.