For uninstalling Snappy: I did a sudo snap list, then uninstalled all packages with sudo snap remove [PackageName] and then I did a apt purge snapd. But it seems still a few packages are installed:
It's not broken, it's just the chromium.deb only contains chromium. It does not contain any of chromium's dependencies, which need installing first / alongside it.
You should run the dpkg command again, exactly as you did previously, and once it finishes listing the unsatisfied dependencies, run this command:
sudo apt-get -f install
This will pick up where dpkg finished, install all the missing dependencies, and then also automatically re-run the dpkg command to install chromium for you.