It took me too long to figure this out, and the documentation wasn’t as clear as it should be. This is how the port bindings map out when using docker-compose with wikijs:
config.yml -> host = docker-compose.yml -> left side of : in the ports section of the wikijs image
config.yml -> ports = docker-compose.yml -> right side of : in the ports section of the wikijs image
Here’s an image to make it more clear.