Instead of up- and down-pointing chevrons arranged compactly, one above the other, at the right side of the control, I am getting large "+" and "-" icons side by side, consuming nearly half the width of the control and pushing part of the value out of the window.

I first noticed this in Inkscape, about a year ago. where it pushes useful information off the screen, but as I don't use Inkscape very often I didn't bother to follow it up. However, I have just written  a C++ program using GTK-4 and I am getting the same behaviour.

The latest GTK-4 documentation says nothing about this, and it includes an illustration showing the conventional layout, and saying "The SpinButton widget looks like this:". Furthermore I have not seen any comments about a change of design on the Internet, so I conclude that this is the result of a fault within my system, perhaps this is a fallback option which is used when a required resource is missing.

I have used strace to verify where configuration, icons and theme are loaded from. I have downloaded the latest icons, which has no effect at all, I have installed a theme (Nordic) which has made everything darker but not altered the layout. I have set the spinbutton orientation to VERTICAL, resulting in the increase and decrease icons each being placed in its own line above and below the number. This wastes about five times as much screen space, but at least the entire number is always visible.

Now I have run out of ideas, so I am asking, what have I overlooked?

I am running a more-or-less standard, more-or-less current Arch Linux.