You plug in a second monitor to keep a document beside your notes, but both screens show the same thing. That can be a working connection in Duplicate mode. Before changing cables, check whether Windows is using the display mode you intended.
Choose the job for the second screen
In Windows 11, press Windows+P. Duplicate shows the same view on the displays; Extend spreads the desktop across them so you can put separate windows on each. Choose Extend for the document-and-notes example. The option to use only the second screen serves a different purpose: it does not leave both displays available as separate workspaces.
Open Settings → System → Display and use Identify to match the numbered rectangles to your physical monitors. Drag the rectangles into the arrangement on your desk, then apply the change. A screen positioned on the wrong side in settings can make a window seem to disappear in the wrong direction.
Try an ordinary window before your next call
Move a simple notes window across the boundary and back. Move the pointer near the top and bottom of that boundary as well. If one screen sits higher, adjust its position in the display arrangement until the crossing feels predictable. Also check which display is primary and where your usual apps reopen.
For a presentation, Duplicate may be exactly what you want, but anything on that view may appear on the other display. Extend does not decide what a meeting app shares either. Before starting a call, select the intended screen or app in the sharing controls and inspect the preview. Keep private windows away from the view you plan to show.