About a month ago I created a Drupal 9 instance using DDEV. It was fast and easy! I spent about 8 hours over several user sessions on my Linux laptop customizing my content types and views.
Last week I upgraded my Pop! OS (Ubuntu-like) laptop, and had to re-install ddev after the upgrade. When I went back into my local directory and ran ddev start... I was greeted with a clean Drupal 9 installation screen. All of my configuration and content seems to be gone?
What steps are there to troubleshoot lost state information, such as a database or filesystem? Are there any chances of finding my previous changes inside the /.ddev/ folder somewhere?
You apparently lost your Docker volumes (which is where the database is kept). I'm sure there's a way to go back to your backups and find them (they were in /var/lib/docker/volumes), but the real point here is to keep database backups. Use ddev snapshot or ddev export-db from time to time and keep those backups around.
I keep a .tarballs directory in each project where I have a basic ddev export-db output and a files dump. It's worked well.
Note that you wouldn't have to reinstall DDEV after a normal OS upgrade, nor would you have to reinstall Docker. I imagine it's the reinstalling of Docker that got you in trouble.
More ideas: