Double click the titlebar should maximize and make it back to an unmaximized window
I think it used to be the case in the past, but double-clicking the titlebar in evince when the program is windowed should maximized it, and when it's maximized it should get back to a window of the size it was, like most other GTK programs do.
It currently does absolutely nothing on evince 43.1 and a whole 43.1 Gnome environment on Wayland.