Issue in installing devtools in R version 4.0 - r

Question

After updating the R version from 3.5 to 4.0 I am facing installation issues with devtools package.
Having Rtools 4.0 and RStudio-1.2.5042 downloaded and installed.
when I try to install devtools
install.packages("devtools")
I get this message:
WARNING: Rtools is required to build R packages but is not currently
installed. Please download and install the appropriate version of
Rtools before proceeding:
https://cran.rstudio.com/bin/windows/Rtools/ Installing package into
‘C:/Users/shalzsab/Documents/R/win-library/4.0’ (as ‘lib’ is
unspecified) also installing the dependency ‘usethis’
There is a binary version available but the source version is later:
binary source needs_compilation usethis 1.6.0 1.6.1 FALSE
trying URL
'https://cran.rstudio.com/bin/windows/contrib/4.0/devtools_2.3.0.zip'
Content type 'application/zip' length 351089 bytes (342 KB) downloaded
342 KB
package ‘devtools’ successfully unpacked and MD5 sums checked
The downloaded binary packages are in
C:\Users\shalzsab\AppData\Local\Temp\RtmpkhJwos\downloaded_packages
installing the source package ‘usethis’
trying URL 'https://cran.rstudio.com/src/contrib/usethis_1.6.1.tar.gz'
Content type 'application/x-gzip' length 255052 bytes (249 KB)
downloaded 249 KB
The downloaded source packages are in
‘C:\Users\shalzsab\AppData\Local\Temp\RtmpkhJwos\downloaded_packages’
And when I load the package I get this error
library(devtools)
Error: package ‘usethis’ required by ‘devtools’ could not be found
If I try to check the packages in the installation directory
find.package("devtools")
"C:/Users/shalzsab/Documents/R/win-library/4.0/devtools"
For usethis package I get this error
find.package("usethis")
Error in find.package("usethis") : there is no package called ‘usethis’
How can I solve this?