For the record: QGIS 3.2 and Mac OS 10.13.5
I am trying to load the symbols from https://www.mapbox.com/maki-icons/
I have tried creating
/Users/rful011/Library/Application Support/QGIS/QGIS3/profiles/default/svg (Which is the default path for sgv files that I copied from Preferences->Option->System) and copying the .svg files into the directory but I still don't see any more symbols in the style dialogue. (edit: because I was looking in the wrong place).
Where should the files appear in the style dialogue?
I then tried "open library" button -> import/export -> import ... and navigated my way to the directory where the svg files are:
As one can see from the screenshot the files are not selectable in the finder window.
After a bit more research (reading the qgis3 symbol library doc) I tried renaming some of the svg files to .xml and they then became selectable in the finder but when I tried importing them I got a dialogue box with the message "An error occurred during import: Incorrect root tag in style: svg".
I am starting to conclude that QGIS is not expecting one to import .svg files this way. ( edit: this is definitely not the way to do it. THis is for simple markers)