I actually wanted this exact feature. I tried using the feature “if door left open X minutes”, but that doesn’t work if the mode changes and the door is already open. So I wrote my own smart app to do it. Assuming your garage door has an open/close sensor, my app supports two notification modes. You can choose a set of modes or a specific time. When the mode changes to a selected mode or the time hits, it will check the state of the monitored door and alert you if it’s open. I didn’t have it auto-close because I’m just nervous about closing a door on top of someone just because they happened to be leaving.
If you know how to use the dev console to install your own apps, I’m happy to provide the source. Otherwise you’ll have to wait until I’ve tested it a bit more and I’ll submit it for public approval.