Files and videos open on the incorrect monitor with multiple displays
On your Mac mini running macOS Tahoe 26.5, try turning off “When switching to an application, switch to a Space with open windows for the application” under System Settings > Desktop & Dock > Mission Control.
This setting controls whether macOS switches to a Space containing an app’s existing windows. Turning it off may reduce unwanted desktop switching, but it does not guarantee that files open on the monitor where you clicked them in Finder.
For an app that repeatedly opens on the wrong display, Control-click its Dock icon and check Options > Assign To. If available, you can assign the app to a desktop on the intended display. The result depends on the app’s window behaviour and your display and Space configuration.
Also check whether Displays have separate Spaces is enabled under System Settings > Desktop & Dock > Mission Control. Changing this setting affects how desktops and full-screen apps work across displays, so do not change it without considering your current setup.
macOS does not provide a universal setting that guarantees every file or video will open on the display where it was selected or prevents every interruption to a full-screen app. See Apple’s guide to working in multiple Spaces.
You can check System Settings > General > Software Update for available macOS updates. However, unless Apple documents a relevant fix, an update should not be assumed to resolve this monitor-placement issue. See Apple’s macOS Tahoe update notes.
If the problem continues, two details will help narrow down the cause: does it happen with all files and videos or only those opened in particular apps, and does macOS switch to another desktop or Space, or does the file simply open on the wrong monitor without switching desktops?