[2023] New player

Go to your library and right click on your game and select properties. Select Betas and the click the dropdown menu and scroll down until you find Alpha 20.6 and select it. Now you will be locked into the current version until you decide to opt out.

Alpha 21 will go to an opt in experimental version first but when it does eventually get pushed to stable it will auto update your game (if you didn't do paragraph one) and break your save.