Steam Deck Developer Mode does not turn off the read-only filesystem

It was pointed out recently that there's been plenty of confusion on exactly what Developer Mode for the Steam Deck does. Even I've gotten it wrong in the past, so it's time to set the record straight. My friend and YouTube star Gardiner recently pointed it out on Twitter, and it's worth repeating.

Developer Mode enables access to numerous extra options and tweaks on the Steam Deck, as the name suggests it's primarily meant for developers and there's a few bits and pieces in there that might help modders. It does not, however, turn off the read-only filesystem.

The confusion comes from Valve, as originally their developer documentation (almost of us had to go on before their FAQs went live) mentioned this:

Will SteamOS have a read-only immutable OS file system?

Yes. By default the OS updates will be distributed as a whole OS image. But any user can enter a developer mode, which will let them modify the file system and install packages like a normal distribution.

Now though, that's not the case. I sent a quick Twitter post to a Valve developer, who has now updated it and corrected the record to be clearer. This is what it tells people now:

Will SteamOS have a read-only immutable OS file system?

Yes. By default the OS updates will be distributed as a whole OS image, and we recommend installing additional applications via flatpak to avoid issues. If customers want to do more than what’s available by flatpak, they can turn off read-only mode. We don't recommend this though, as they may get their Steam Deck into a bad state or compromise their data. In addition, anything installed outside of flatpak (via pacman for instance) may be wiped with the next SteamOS update. More on that here.

Turning off the read-only filesystem requires a terminal command, which you can find in the previous link. Again, not recommended for the average user.

What does Developer Mode give you? Here's some of the options it currently opens up: