This feels weird to know^[I don’t have a Steam deck] and hard to understand.

1. Steam OS is based on KDE, which, while originally made for PCs, lets all network activity work, with the screen off. You can even set a shortcut key to turn off the screen, which will then turn back on, if you move the mouse or press a keyboard key.
2. Steam on Desktop lets you work with the screen off.
3. ???
4. Steam’s mode made for a device that has to tax the battery to keep the screen on, then goes ahead and removes the ability.