Airplane mode, don’t even bother with offline mode. Some games won’t launch in offline mode but will launch in airplane mode just fine.

What’s the process again to not get screwed over by no internet?

load up with tons of non steam games or emulators. none of those will require internet unless its actually an online game obviously.

Start your games while connected to the internet to make sure they’re updated. Exit them. Turn off internet/activate airplane mode. You can now play offline with no problems, fully shut down the deck and turn it back on if you want, and should be good to go in every way.

That’s airplane mode, not offline mode. I don’t really know what Valve’s offline mode and it seems weird and inconsistent. Simply turning off the device’s internet connection is where it’s at.