What's happening is that shader effects (such as the caustics and the mist) do not work on any of my Linux systems when run through Wine.
Here's a screenshot of the Linux-native version of the editor and the game running in Wine (with the editor showing the screen effects set to Underwater). Note that the wavy effect does work, but the underwater caustics effect doesn't.

I recall it working fine in earlier versions of Wine (it definitely worked in Wine 7.2), but I don't really want to have to run the game through Lutris all the time just to make the shaders work (especially when testing levels).