I remember in the past, we can double click the "highlighting icon" and make it a highlighting mode, so whatever we select in the PDF document, it'd be highlighted permanently. Select something again, and it is again highlighted permanently. (highlighted as if it is marked by a highlighter).
But now in Mojave, it doesn't seem to have this mode? We have to select something and move the mouse to click that highlighting icon, and select some text, and move the mouse to click that highlighting icon again?