Julia must be installed separately in order for the JuliaConnectoR package to work. You can download and install Julia from https://julialang.org/downloads/.
If you have installed Julia via Juliaup, the Julia installation should be discovered by the JuliaConnectoR.
If you have freshly installed Juliaup, start Julia once on the command line.
This will do the actual installation of the current Julia version.
Juliaup puts the Julia executable on the system PATH.
This way, the Julia installation can be detected by the JuliaConnectoR.
After the installation of Juliaup, Julia might not be on the system PATH
but it should be discovered automatically
if it is installed in the default location, i.e., the .juliaup
folder in your home directory.
If you have installed Julia via a binary package or any other method,
the simplest way to make Julia discoverable is by adding the directory
containing the Julia executable to the PATH environment variable.
Alternatively, you can set the JULIA_BINDIR environment variable
to specify the exact directory containing the Julia binary.
(You can find the correct path to this directory by evaluating the expression
Sys.BINDIR within Julia.)
If the JULIA_BINDIR variable is set, it takes precedence over
looking up the system PATH.
This makes it easy to use a different Julia version
than the one in your system PATH.