If you use emudeck it comes with a tool called steam rom manager that lets you easily add the emulators to steam and you can launch them in gaming mode super easy. The only one that had issues was mariokart but that’s because emudeck picked the wrong game file to try and launch so I edited the launch commands to the correct file name and it works perfectly now.
Hold on. You ordered a second deck entirely? Just in case? How does that work? Are you going to send one back if they’re both fine?