How to import GarageBand files into Logic Pro?

Launch Logic Pro. If you are given the option to open a new file, then simply navigate in the "Open File" dialog box to the Garage Band file and open it.

If you already have Logic Pro open, close any currently open projects. Then click File > Open and navigate in the "Open File" dialog box to the Garage Band file and open it.

You will be prompted to convert the file to a Logic Pro project. Allow that and you can continue on your way.

GarageBand projects in Logic Pro for Mac - Apple Support

You're welcome.

Re: conversion of the project... Logic actually leaves the original GB project file untouched but processes its data internally into a project that you will save as a Logic project. But it's never a bad idea to create a copy of any project or to have backups.

And no, work done in Logic is not backward compatible with GB. Logic cannot save or export a Logic project as a GB project file. Collaborators will need to have their own installations of Logic Pro.