I usually don't do Mac exports, but I always do a Linux version (statistically there are more Linux Steam users than Mac), especially nowadays with Steam Deck.
I haven't tested WebView2 yet, but I think there are a few main things to consider:
1. The obvious Steam overlay and SDK support.
2. File handling should have more features. Getting the OS %USER% and %APPDATA% directory and saving/loading files directly to them without having to select the folder manually.
This is crucial for Steam cloud save support and for managing local game data.
3. It should work well with video capturing apps, such as OBS and the built-in Nvidia recorders. I'll point out that capturing from NWjs is smoother than from a chrome browser. Not sure why that is.
4. Control over the window, such as setting the window size or starting the app maximized.
5. Fullscreen command should work without user input.
Last but not least, performance should be at least equivalent to NWjs.