R - Why can I not install devtools and neither some of its dependencies?

Question

I am trying to install devtools and I think the problem is with its dependencies. I also tried to singularly install processx but I got still error. Thank you so much.

 * installing *source* package ‘processx’ ...
    ** package ‘processx’ successfully unpacked and MD5 sums checked
    ** libs
    xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
    ERROR: compilation failed for package ‘processx’
    * removing ‘/Library/Frameworks/R.framework/Versions/3.4/Resources/library/processx’
    Warning in install.packages :
      installation of package ‘processx’ had non-zero exit status
    Warning in strptime(xx, f <- "%Y-%m-%d %H:%M:%OS", tz = tz) :
      unknown timezone 'zone/tz/2019c.1.0/zoneinfo/Asia/Bangkok'
    * installing *source* package ‘usethis’ ...
    ** package ‘usethis’ successfully unpacked and MD5 sums checked
    ** R
    ** inst
    ** preparing package for lazy loading
    Error in loadNamespace(i, c(lib.loc, .libPaths()), versionCheck = vI[[i]]) : 
      namespace ‘fs’ 1.2.7 is being loaded, but >= 1.3.0 is required
    ERROR: lazy loading failed for package ‘usethis’
    * removing ‘/Library/Frameworks/R.framework/Versions/3.4/Resources/library/usethis’
    Warning in install.packages :
      installation of package ‘usethis’ had non-zero exit status
   ERROR: dependency ‘processx’ is not available for package ‘callr’
    * removing ‘/Library/Frameworks/R.framework/Versions/3.4/Resources/library/callr’
    Warning in install.packages :
      installation of package ‘callr’ had non-zero exit status
   ERROR: dependency ‘callr’ is not available for package ‘pkgbuild’
    * removing ‘/Library/Frameworks/R.framework/Versions/3.4/Resources/library/pkgbuild’
    Warning in install.packages :
      installation of package ‘pkgbuild’ had non-zero exit status
    ERROR: dependencies ‘callr’, ‘pkgbuild’ are not available for package ‘rcmdcheck’
    * removing ‘/Library/Frameworks/R.framework/Versions/3.4/Resources/library/rcmdcheck’
    Warning in install.packages :
      installation of package ‘rcmdcheck’ had non-zero exit status
    ERROR: dependencies ‘usethis’, ‘callr’, ‘pkgbuild’, ‘rcmdcheck’ are not available for package ‘devtools’
    * removing ‘/Library/Frameworks/R.framework/Versions/3.4/Resources/library/devtools’
    Warning in install.packages :
      installation of package ‘devtools’ had non-zero exit status

    The downloaded source packages are in
        ‘/private/var/folders/75/5wf3rrn96jj16b19vf_5j_600000gn/T/RtmpTQ6FNv/downloaded_packages’