I simply missed that question, sorry for that
All that time I have been using drag & drop from FreeCommander or a send-to shortcut in FreeCommander. I also tested just now drag & drop from Windows Explorer - still nothing. But when I use now the "Add directory..." icon within Mp3tag, the WEBM files finally get loaded to Mp3tag
So. Does point into the direction of having something to do with what I ask about at the top of post How to send and drag & drop files to an audio editor? -OR- Problems with running as (not) administrator on Windows 10 - #5 by Zerow above the [That would be a first solution] statement?
But both my Mp3tag and FreeCommander [and also explorer.exe] are shown to be running as No in the
Task Manager > Details > Elevated
And now, that I can finally load WEBM files at least in one way, what I have noticed in regards to
The WEBM files do not show to me theirs lengths- which is to be expected, as the supported video file format is MKV, right? But when those very same files are renamed be me into MKVs, they suddenly gain the ability to display length. [Although I cannot rename them without issues from within Mp3tag - the files must be tampered with in FreeCommander of Windows Explorer]
So once again: why al this pretending or "pretending" or whatever it might be called, that Mp3tag does not handle videos other than MKV?