I’d suggest that you use dbpoweramp.
If Audacity is unable to recognize an audio format even though FFmpeg is installed, it means that the installed version does not support that format, in which case the only solution is to convert with some other application. In your case, you said that dbpoweramp works.
Audacity seemingly can open these files as various thread on this, and other forums, show so rather than pithily telling me to go use a different program I would have thought you would want to help solve my issue not least so anyone else with my issue can benefit from this thread but then again what do I know.
I’m assuming that you have FFmpeg correctly installed and working.
You can check that as follows:
“Generate menu > Chirp”, then “OK” (default settings create a 30 second rising tone)
“File menu > Export > Export Audio”
Select “M4A (AAC) Files (FFmpeg)” as the file type, and complete the export.
If you are able to export as M4A, then FFmpeg is working correctly.
If FFmpeg is working correctly but Audacity is unable to import a particular file (“Audacity did not recognize the type of file”), then that means that particular file is not supported by Audacity’s version of FFmpeg.