We're going into ridiculous territory of tweaking now and the possibilities are seemingly endless on what you can do with the Steam Deck. You can even run the Desktop Mode inside of Gaming Mode.
Thanks to a Reddit user, the script is pretty simple and only needs you to add the commands into a text file, set it as executable and add it to Steam as a Non-Steam game. From there, you can launch and switch between desktop mode and games running in the background and it actually works. It's far from perfect with some issues where the desktop mode may freeze up so you need to quit it with certain games, and sometimes the mouse won't go to the very bottom but hey — this is the kind of awesome stuff you can do with Linux right?
Here's a brief demo:
Love it. If you try it, don't blame me if you break something. Just wanted to highlight something mildly amusing and also somewhat useful too.