Failing to install rClr in Ubuntu 19.04

[PavelBal]

I have a clean installation of Ubuntu 19.04. I have installed Mono as described here:
https://www.mono-project.com/download/stable/#download-lin

When trying to install rClr, I get the error:

"msbuild" rClr_monodev.sln /t:Rebuild /p:Configuration=Unix /p:Platform="Any CPU" /nologo /consoleloggerparameters:ErrorsOnly /verbosity:minimal
if [ -e symbols.rds ] ; then cp -u -p symbols.rds ../inst/libs ; fi
# using rm -f to prevent the following, which seems to occur even when these should not be write-protected
#  cp: cannot create regular file `../inst/libs/ClrFacade.dll': Permission denied
rm -f ../inst/libs/*.*
cp -u -p ./Release/*.dll* ../inst/libs
cp: cannot stat './Release/*.dll*': No such file or directory
make: [Makevars:134: rClrLib] Error 1 (ignored)
installing to /home/pavel/R/x86_64-pc-linux-gnu-library/3.5/rClr/libs
** R
** inst
** byte-compile and prepare package for lazy loading
** help
*** installing help indices
** building package indices
** installing vignettes
** testing if installed package can be loaded
Error: package or namespace load failed for ‘rClr’:
 .onLoad failed in loadNamespace() for 'rClr', details:
  call: clrInit(debug_flag != "")
  error: file.exists(f) is not TRUE

It seems that after calling
"msbuild" rClr_monodev.sln /t:Rebuild /p:Configuration=Unix /p:Platform="Any CPU" /nologo /consoleloggerparameters:ErrorsOnly /verbosity:minimal

no files are created in ./Release/.dll.

What are the exact dlls that have to be compiled during this step? Don't we need to compile rClr.sln? How should ../inst/libs look like at the end?