I was able to get it to work (at least for the five minutes so far that I've played it) using Proton with the following steps:
1. Download and install the Windows build.
2. Add it to the Steam launcher as a non-Steam game.
3. In Steam, right-click on the entry and select Properties.
4. Edit 'TARGET' to point to SCU.exe and "START IN" to the installation directory. (This may have been done for you automatically but I had to go back and do it by hand.)
5. Select "Compatibility", check the "Force the use..." checkbox and select "Proton 6.3-8". (Other versions may work as well or better; YMMV.)
The one thing that doesn't work is the menu backdrop. That's apparently a video playback issue in Proton. Other than that, I was able to walk around the mall pretty well.
I also tried it using stock wine (Ubuntu 20.04, Wine 5.0) and it runs (including the video, oddly enough) but a lot of the textures are missing during play.