none of the suggestion helped me, so what I did was the easiest thing, I uninstall the gboard, then I re installed the gboard and selected the gboard as keyboard, and the microphone was back on my key board. hope this helps.
Thanks for the tip, the pink line went away when I did the test interface. But seeing some of these other messages, the test interface is just a temporary fix? This is the first time the pink line happen to me, lets hope it does not come back.