Second monitor not showing loupe

[hifiguymn]

I just installed a Benq 270c as a second monitor. It's connected via usb c to my Surface Book 2. I can drag the the library view from monitor 1 to monitor 2, but when I select monitor 2 the loupe view stays on monitor 1.

I suppose I have a setting wrong, but have no idea where to look.   Yes, I have closed and restarted several times, no change.

Suggestions?

[Per Berntsen]

You can choose monitor for secondary window under Edit > Preferences > Display.

If you want to move a full screen secondary window to the other monitor, press Shift + F11, then drag the window.

To make it full screen on the other monitor, press Shift + F11 again.

[HiFiPete1999]

Thanks very much.