Ok I found the issue. There is an extra set of MS fonts sitting in /Library/Fonts/Microsoft. There is also another set sitting in /System/Library/Fonts/Supplemental, which I believe is the default location. I checked another Mac where RStudio output is working if the /Library/Fonts/Microsoft exists. It does not so as soon as I move the Microsoft folder out of /Library/Font and restarted Rstudio, the tibble output started showing properly.