You can play this game through the official website and through Steam.
Please note that if you play through Steam, you will be playing on the game's test servers, not the official ones.
To the original servers: (Ref link) https://www.milkywayidle.com/?ref=149737
To the original servers: (No Ref link) https://www.milkywayidle.com/
To the test servers through Steam (not recommended): https://store.steampowered.com/app/32244..._Way_Idle/