TL;DR: You can't shrink it, but you can keep it from growing by proactively pruning unused images. You can also delete it, and recreate it with a lower maximum size. By default it will grow until 100GB and then throw out-of-space errors when you try to download/create additional images.

So when I’ll be at 100 GB, just uninstall and reinstall Rancher-Desktop, right ?