How do I switch a Steam client to windowed mode?

[Денчик]

Clarification: not launching games in windowed mode, but the client itself. It used to run in a window. Now it runs in full-screen mode and does not translate into windowed mode in the standard way.

[Cathulhu]

Do you mean Big Picture mode? Disable that in the settings.

[Денчик]

Not. This is a common function for all windows in system. In the upper right corner there are offset squares in full screen mode and a single square in windowed mode. In the window, you can change the size of the window with the mouse.
For a Steam client, the window size does not change when the mode is changed. And you can't change it with the mouse either (the mouse cursor does not change to a double-headed arrow.

[cSg|mc-Hotsauce]

If the double squares are present, move the window itself over to one side and then shrink it manually.

[Jaunitta 🌸]

Esc to window drag bottom right corner inwards to reduce to what you want

[Денчик]

Originally posted by cSg|mc-Hotsauce:

If the double squares are present, move the window itself over to one side and then shrink it manually.

Happened. Strange behavior. I used to fold without problems.

[Silicon Vampire]

I’ve seen this appear many times over the last decade+ and it always irks me but is insignificant to all the other issues over that same period.