Not to worry! Accessing it is as simple as it was the last time it was removed. Navigate to the local files (manage local files through steam), and open the .exe. This will launch the game.

The demo was taken off the steam page indefinitely because of the new fee structure Unity is introducing. It is unclear if it will make an official return. In the meantime, you are able to download copies from the internet archive, you can find such copies in the resources section of this leaderboard, or the resources channel in the discord.