RStudio & Rcmdr: Installation problems w/ tcltk2 on Kubuntu 20.10 Desktop

First, on Linux Mint 20 the installation of Rcmdr is no problem at all. But on Kubuntu, it is. When you try to install Rcmdr from within RStudio by

install.packages("Rcmdr")

you may run into the error msg:

Error: package or namespace load failed for ‘tcltk’:
.onLoad failed in loadNamespace() for 'tcltk', details:
call: fun(libname, pkgname)
error: Tcl/Tk support is not available on this system
Error: package ‘tcltk’ could not be loaded
In addition: Warning message:
S3 methods ‘as.character.tclObj’, ‘as.character.tclVar’, ‘as.double.tclObj’, ‘as.integer.tclObj’, ‘as.logical.tclObj’, ‘as.raw.tclObj’, ‘print.tclObj’, ‘[[.tclArray’, ‘[[<-.tclArray’, ‘$.tclArray’, ‘$<-.tclArray’, ‘names.tclArray’, ‘names<-.tclArray’, ‘length.tclArray’, ‘length<-.tclArray’, ‘tclObj.tclVar’, ‘tclObj<-.tclVar’, ‘tclvalue.default’, ‘tclvalue.tclObj’, ‘tclvalue.tclVar’, ‘tclvalue<-.default’, ‘tclvalue<-.tclVar’, ‘close.tkProgressBar’ were declared in NAMESPACE but not found 
Execution halted
ERROR: lazy loading failed for package ‘tcltk2’
* removing ‘/home/hmb/R/x86_64-pc-linux-gnu-library/4.0/tcltk2’
Warning in install.packages :
installation of package ‘tcltk2’ had non-zero exit status
ERROR: dependency ‘tcltk2’ is not available for package ‘Rcmdr’
* removing ‘/home/hmb/R/x86_64-pc-linux-gnu-library/4.0/Rcmdr’
Warning in install.packages :
installation of package ‘Rcmdr’ had non-zero exit status

This most probably means that your system is missing the libs

tcl-dev

and

tk-dev

Install them using

apt-get install tcl-dev tk-dev

Now rebuild R (make, ./configure…).

Afterwards RStudio should be able to let you install the package tcltk2. And as a consequence, you should be able to install Rcmdr, too.