Mac OS keyboard viewer doesn't highlight trackpad taps
Since upgrading to Mojave the keyboard viewer on my iMac doesn't highlight letters as they are tapped on my Magic Trackpad. However, the letters are highlighted as intended if clicked with a mouse. The keyboard viewer worked properly with mouse/trackpad in older versions of Mac OS.
This is more annoying than critical as the keyboard viewer still works, but it's harder to tell if a tap has registered. If there isn't a known fix for this now, hopefully it will be addressed in future OS updates.
iMac Line (2012 and Later)