[KevinH]

Is there any size or scaling difference between the Sigil MainWindow when it has no menubar to the version you recover by minimizing and restoring it to bring the menubar back/ Perhaps a larger or smaller scaling? Or maybe an small positional offset?

It does sound as if anything that will cause the MainWindow to be redrawn will work to return the menu bar. So something is causing a refesh/update signal to get lost when the KVM switch is thrown.

By any chance is your linux box set to use a single top menubar (like the macOS does)? Some KDE and GNome desktops can be set that way.

As to why the menu bar goes away at all, probably has to do with detecting changes in how different OS's use different monitor resolutions/refresh rates on the exact same monitor when connected to the switch.

So you might try syncing the Linux driver resolution and refresh rate, and scaling to **exactly match*** those used by Windows and see if the issue goes away.

I have no idea how the Qt software or Windows monitors for changes in these settings *not* caused by manually setting those values in the control panel (ie how it detects the KVM switch was thrown)

The KVM switch must be responsible for telling the Monitor to autosync and then alerting the OS somehow.