How to I get Big Fish to work on Ventura 13.1

An answer depends on which games you want to play.

In case you missed it, please refer to this excerpt from Big Fish Games Help:

Updated information for macOS Catalina!

With the release of macOS Catalina (10.15), Apple has made the decision to stop support for 32-bit apps. This means that systems running macOS Catalina (10.15) and newer will not be able to play our 32-bit games. 

Check out our instructions about how to download and play select games 64-bit apps on macOS Catalina! 

To learn more about macOS Catalina, please read our help article.

There is also some updated information here: macOS Update – January, 2022

The most applicable information is likely what Sparks0829 wrote: the only games guaranteed to work will be found on the Mac App Store, here: Big Fish Games, Inc - Mac

Hi there Groovy_Granny,

When you say you have Big Fish downloaded on your Mac, where did you get it from exactly? We ask because Big Fish is an app developer, and not an actual app itself. To download apps from that developer, you can visit the Mac App Store and download the games in the Mac section. Have a look at this link: Big Fish Games, Inc - Mac

Take care.