R version 4.1.1 (2021-08-10) -- "Kick Things"
Copyright (C) 2021 The R Foundation for Statistical Computing
Platform: x86_64-w64-mingw32/x64 (64-bit)

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> install.packages("Rcmdr")
Warning in install.packages :
  'lib = "C:/Program Files/R/R-4.1.1/library"' is not writable
Error in install.packages : unable to install packages
Making 'packages.html' ... done

This support site is intended to help people with Bioconductor packages, and Rcmdr is a CRAN package. In future you should ask about CRAN packages on r-help@r-project.org.

That said, the default library directory on Windows is not writeable by a regular user, and when you try to install packages you should get a message asking if you would like to use a personal library instead. You should say 'Yes' to that, otherwise you won't be able to install any packages.