Update 1.1.83 added support for controllers https://forums.factorio.com/viewtopic.php?f=3&t=106660

Added controller(gamepad) support. Change input method in Settings->Controls to play using a controller.

From the devs about the steam deck https://forums.factorio.com/viewtopic.php?p=586148#p586148

On Steam Deck you need to change the configuration to “Generic Gamepad” or “Gamepad with Mouse Trackpad”.

Nothing so far. They are tight lipped about it. I do wonder if you could glean some information by looking at what bugs they are fixing that are not reported on the forum.

It has been a while since they updated this frequently.