I've tried a few different CRAN mirrors but all return the same issue. I can install from sources, but sometime this will fail if the dependencies can't be installed from source.
Looking at the URL provided, it doesn't seem like /PACKAGES directory exists. Anyone have an idea about what is going on and how to fix this?
I've seen a lot of this today. Problem probably originates with CRAN having a problem with their MAC binaries directory and it propagating to the mirrors. You may have some luck compiling from source, but due to Apple's non-standard clang implementation that may not go well.
The package index file PACKAGES is missing in the binary repository for R 3.6.x due to a sync issue yesterday (the build machine was relocated yesterday). This has been fixed now, but it may take CRAN mirrors some time before the change propagates, so please use the master https://mac.R-project.org
as the CRAN mirror until it does.