I see no evidence for this, and plenty of evidence to the contrary. Notably, after the initially failed Steam Machines, we now have Steam Deck, Steam Machine Mark II, Steam Frame, Steam Controller Mark II, etc.
And critically, Valve seems to be learning, iterating, and the Steam Deck and Steam Controller Mark II are both much more enjoyable to use than the first Steam Controller.
From their perspective, Valve are otherwise dependent on Microsoft or Apple who see them as competition to squeeze out. Success of the Steam hardware platforms is their only way to change that situation. Therefore all evidence points to Valve continuing to iterate until they find success. They are a private company, so they can afford to do so indefinitely without worrying about pissing off a board or investors.