Maybe I have a hole in my understanding, but I thought(!) .mid and .smf were just two different file extensions for the same file format.

Certainly if I run the Linux "file" command on some .mid files, they get reported thus:

$ file *.mid *.MID
drum_patterns.mid: Standard MIDI data (format 1) using 2 tracks at 1/480
thejourneyhome.mid: Standard MIDI data (format 1) using 11 tracks at 1/120
Moondance.MID: Standard MIDI data (format 1) using 9 tracks at 1/960

I've just run file $(find . -name "*.mid") on a file tree and I believe every file reported as "Standard MIDI data...". There are hundreds. I haven't found any .smf files on my machine to compare.

Maybe if you're on Windows, which relies on file extensions rather than file formats, it's just that it isn't recognising the file for what (I think) it is.

Try just changing the file extension.

Jazz relative beginner, starting at a much older age than was helpful.
AVL:MXE Linux; Windows 11
BIAB2025 Audiophile, a bunch of other software.
Kawai MP6, Ui24R, Focusrite Saffire Pro40 and Scarletts
.