Unable to switch input sources after updating macOS to 10.14.6
I had the same issue with my mbp after the update. I called Apple support and they said it might be a software glitch that prevent this function from working. The solution I got was shutdown the computer, press the start button and as soon as I let go, press ^control+⌥command+P+R at the same time for 15-20 seconds, and login as usual. It solved my issue.