What this little demo project does is register functions of my application with MacOS, so that when a disk appears, disappears, or changes, my application gets notified by the OS.
For this I have used what Apple calls "DiskArbitration". I've included the required units for that (diskarbitration and dissenter).

The demo also shows how to read a CFArrayRef and how to convert a CFStringRef to a Pascal string;

function CFStringToPascalString(theCFStringRef: CFTypeRef):string;
var FBuf : array of Char;
begin
  if theCFStringRef<>nil then
    begin
      FillChar(FBuf, SizeOf(FBuf), 0);
      CFStringGetPascalString(theCFStringRef,@FBuf,SizeOf(FBuf),CFStringGetSystemEncoding);
      Result := trim(StrPas(PChar(@FBuf))); // skip 1st char, it's a strange 1st char causing crashes
    end
  else
    Result:='';
end;           

I hope it is to use for one or the other Lazarus Pascal user that works under MacOS.