Yes, that's it. I ran a few tests.
1. Win+L (Win 11) plus turn off both monitors.
2. Turn on monitors and log in.
WinScp is now in the far right position in the menu bar (even if it was somewhere else before) and displays the default icon.

As you can imagine, this behavior is very difficult to observe directly. However, I think that yesterday evening the icon in the menu bar (rightmost icon, no “...") was still displayed correctly, but this morning it appeared as the default icon. Overnight, I lock Windows with Win+L and turn off the monitors. (But that's not the only way the icon gets lost.)

The icon reappears when you bring the application to the foreground and click on the passive side. This probably triggers a window refresh, which also displays the icon in the menu bar correctly again.

Thanks. Please let me know if you observe when the icon is lost.

I lost the correct icon several times. However, it also returned on its own. Unfortunately, I did not observe this live.

But now I was able to see it return. It was when I copied a file from the right (Linux) to the left (Windows) window by pressing F5. Something at the end of the copy process brought the icon back.

Ok, thanks. Please let me know.

Thanks for looking at this report.

First, the wrong icon was not only in the "…" menu of the taskbar, but also normally on the taskbar when I closed a few applications.

Anyway, I stopped and restarted WinSCP. Now the icon appears correctly in all locations. I briefly tried to reproduce the behavior described, but unfortunately (or fortunately?) without success. Maybe I will be able to observe the behavior again at some point and say more about it.

Thanks for your report. Though I cannot reproduce it. Does the wrong icon appear as soon as you start WinSCP? Or does it break only later? When?

I'm using WinSCP 6.5.3 under Win 11 [Version 10.0.26100.6584].

If my taskbar is full, a menu '…' appears at the right end of the taskbar. Clicking on it I see the open programs with the specific icon. But WinSCP use a standard icon. As you can see in the attached screenshot 7zip does it right (and all others too).

Well, it's not a bad thing, but definitely nice to have. ;-)