Click OK . GOG Galaxy will download the legacy framework files for you. Modding the Compatibility Version (Important Warning)
Modern versions of Stardew Valley require a 64-bit operating system. If you are on an older 32-bit Windows or Mac computer, the standard game will not launch. Stardew Valley Compatibility Version Download
If you do not see the compatibility branch in Steam, restart your Steam client. If it still doesn't appear, ensure you are logged into an account that fully owns the game. Save Game Compatibility Click OK
Here is how to download it and what you need to know before switching. How to Download the Compatibility Version Open your and right-click on Stardew Valley . Select Properties , then navigate to the Betas tab. then navigate to the Betas tab.