https://unix.stackexchange.com/a/624808/ says:
A simple way:
cdinto the directory of the files- Run
ffmpeg -f concat -safe 0 -i <(for f in ./*.mp3; do echo "file '$PWD/$f'"; done) -c copy ./output.mp3This only works if you cd into the actual directory and not to a shortcut to it.
More at the ffmpeg wiki page on Concatenate
Why is "This only works if you cd into the actual directory and not to a shortcut to it"?
It works for me when I cd into a folder of the files via a softlink to an ancestral folder.