Name the launch route that failed
Opening VLC twice and double-clicking a second media file are different actions. The desktop 3.0 Windows guide documents separate instance controls, including the file-manager path. Record which route sent the file to the existing window.
Review both relevant values
Inspect the general single-instance preference and the file-manager instance preference in the installed Interface settings, then save the intended values. Preserve the previous configuration. Do not infer Windows behaviour from a macOS workaround or assume the same labels across every platform.
Rehearse one owned sample opened through the application and another through the actual file-manager route. Note where each appears and which window has focus. No launch test was performed for this article.
Keep audio and focus understandable
If independent sessions now open, pause or mute one while comparing sound. Record which edit belongs to each window. The goal is predictable launching, not an unsupported claim that the two sessions are synchronised or that the machine can decode any pair concurrently.
Questions answered
Does allowing a second app instance necessarily cover every file-manager launch?
Review the documented separate file-manager preference and the actual route used.
Does this article establish the same workflow on macOS?
No. Its checked scope is VLC desktop 3.0 on Windows.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.