To export your Google Maps starred locations:
Go to Google Bookmarks: https://www.google.com/bookmarks/
On the bottom left, click "Export bookmarks": https://www.google.com/bookmarks/bookmarks.html?hl=en
After downloading the html file, run this script on it to generate a KML.
It's hacky and doesn't work on all of them, but it kinda works.
I made a Python 3, GeoJSON-exporting version based on this script here:
https://gist.github.com/jbg/60bf54b8f19c0a42abf7091c486d17fc