For most documents file types (txt, pdf, docx, etc), 'Open' is the "default" (marked in bold) action and resides at the top of the context menu in Windows 10.
I am pretty sure that this was also the case for media file types until recently when something caused the 'Open' menu item to drop down in the list and for the 'Open with' to become the "default" entry.
Among recent changes were installing Winamp and adding custom context menu entries for a few tools (Spek, MP3Gain) via the registry (albeit the latter change was done on an extension basis and only for a select list of audio types). Not sure if any of those changes caused this, and if so, which ones.
Regardless, how can I reset the 'Open' menu entry to be the "default" one and to restore its position as the topmost entry in the context menu list?