SUMMARY
Since I think this commit https://invent.kde.org/frameworks/breeze-icons/-/commit/4c44c5a02464053bd082610689e549deffdce91e (although maybe also an earlier one, I'm not sure), GTK 2 and GTK 3 applications display an X in place of a minus or a down pointing arrow for spinboxes. I manually applied this patch https://invent.kde.org/frameworks/breeze-icons/-/commit/ff1ccc38f1b2d1708935566d3d5e55d30ce57b21 since it seems the intent was to fix this issue, but the problem persists.

I understand the nomenclature is now correct, but GTK 2 and GTK 3 will not fix this, since they're end of life, but applications written in those toolkits will still exist and be widely used for a long time, so Breeze icon theme should still display the correct icon also for them. Having an X icon in this context doesn't only look very weird aesthetically, but it confuses less experienced users and makes it very hard to support them by giving instructions.

STEPS TO REPRODUCE
1. Set Breeze as the GTK 3 and/or GTK 2 icon theme.
2. Open GTK 3 and/or GTK 2 application that has spinboxes.

OBSERVED RESULT
The button to decrease the number of the spinbox is the X symbol instead of a - or a down-pointing arrow.

EXPECTED RESULT
The decrease button should have a - or a down pointing arrow. Never an icon that means something else.

SOFTWARE/OS VERSIONS
KDE Plasma Version: KDE 6.2.0/6.2.2
KDE Frameworks Version: 24.08.x