I installed the arrow R package version 4.0.0 from CRAN on an Intel Mac that does not have pkg-config installed, and I saw this in the installation log
This is happening because of line 79 and 80:
The first conditional on line 80 causes $? to be set to 0, so then the second conditional evaluates to true. Reverse the order of these two conditionals so that $? truly reflects whether pkg-config is installed.