Hello!
This is covered in the instructions above. I also just tested Mint 21.1 and everything is still working for me.
Sorry, but I don’t understand the context of your question. Why are you looking for snap help refresh? Our documentation on controlling snap updates can be found here: https://snapcraft.io/docs/keeping-snaps-up-to-date
I’m not sure why the snap is not currently available (I can’t install this either). Hopefully this is just temporary.
For me on Mint, the deb has a single dependency of libphysfs1, which needs to be installed first:
sudo apt install libphysfs1
sudo dpkg -i warzone2100_ubuntu20.04_amd64.deb
The game then works.