Music won't import an mp4 song?

For the life of me I can't get Music to import an mp4 song.

It lives in a folder on my MacBook. If I double click it Music will play it just fine. I want to import it into my music library so I can then play it on my iOS devices.

I launch Music, go to File, select Import, navigate the nested folders to find the music file, highlight it, and click Open.

[Aside, why the blank it say "Open" instead of "Import" I don't know. I want to IMPORT it to Music, NOT open it. But I digress.]

And.....nothing happens. Nothing. I've repeatedly done the above while expecting it to work (which is one definition of insanity and, yes, Apple, as usual you are driving me crazy).

Please, someone tell me how to import one single, solitary, 38 second mp4 sound file into Music, because the task is evidently beyond the capabilities of this 35 year Apple veteran.