Hi, and welcome!
Please see the FAQ: What's a reproducible example (`reprex`) and how do I do one? Using a reprex, complete with representative data will attract quicker and more answers. Not needed for this type of question, though.
The short answer is that things went south when accepting the offer to install from source. Sometimes things go smoothly, and often you get the dreaded non-zero exit status or, configuration failed.
This is due to Apple's non-standard compiler. St. Simon Urbanek of the R Core Development Team relieves MAC users like us of the brain damage required to edit the source code to allow it to compile on our machines and provides binary versions. Normally, this takes 7-10 days after a new CRAN version appears. devtools versions don't get that love, however.
I'm happily using sf_0.8-1 in binary, and it happily chirps Linking to GEOS 3.7.2, GDAL 2.4.2, PROJ 5.2.0.