If appears that recent versions of XOJO (I’m using 2025 r1, but I don’t know when the bug was introduced) have an automatic repetition of user added menu items: the list of user added windows. The attached screenshot, using the unmodified Window Menu example file that comes with Xojo, shows the effect. The problem does not affect Windows version of the same app, nor does it affect programs compiled with older versions of Xojo that use the exact same mechanism to add windows to the Windows Menu.
Happy to add this to feedback if this is truly a bug and not a known effect of the new features added to the Windows Menu on the Mac.