If you are referring to the mIRC button that appears in the Windows taskbar, mIRC has no control over this. The way this works is controlled entirely by Windows, including the mouse-over. It has never been possible to access the mIRC settings through this button.
However, if you have enabled the Tray feature in the mIRC Options/Display/Options/Tray dialog, this will display a small mIRC icon in the Windows tray, at the very right of the Windows taskbar.
It also may be that your Windows 11 is not displaying all application tray icons. You can right-click on the Windows 11 taskbar, select "Taskbar settings" and in the "Taskbar corner overflow" options, you can specify which application icons can appear in the tray area.