I think you misunderstood #32129.  It was specific to macOS Aqua systems.  On Windows and generally on Linux, window title bars have a little icon on the left end (at least on Windows).  IDLE uses the tcl/tk GUI framework and by default, on these systems, tk windows have a generic tk icon at the left end.  (At least that is the position on Windows.) #20406 replaced the tk icon with versions of the Python app icon.

On mac Aqua, tk window title bars do not have an icon.  Somehow Mac, Aqua, and tk interact so that the replacement icon instead replaced Apple's version of the Python app (menu) icon, which is different from the *nix/Windows python app icon. This was unintended and a bug.  The fix was to not execute the replacement code on Mac Aqua systems.

Your png shows the Python app icon used for IDLE as a Python application.  It is the same one used for Python applications on the Windows taskbar, including but not limited to IDLE.  I agreed on #32129 that it would be good if someone contributed higher resolution versions.  But it is not specifically an IDLE issue.  I will say more tomorrow.