The problem is very very strange.
When I open RStudio, it tells me the package "questionr" is not installed and ask me if I want to install it (because my script mentions it and it's not installed), in the pale yellow banner above the script window.
If I click "Install" (instead of write it with the function "install.package"), it installs it 
Installing 'questionr' ...
Installing package into 'C:/Users/Gloubi/Documents/R/win-library/3.6'
(as 'lib' is unspecified)
There is a binary version available but the source version is later:
binary source needs_compilation
questionr 0.7.3 0.7.4 FALSE
installing the source package 'questionr'
essai de l'URL 'https://cran.rstudio.com/src/contrib/questionr_0.7.4.tar.gz'
Content type 'application/x-gzip' length 1714911 bytes (1.6 MB)
==================================================
downloaded 1.6 MB
The downloaded source packages are in
'C:\Users\Gloubi\AppData\Local\Temp\RtmpcLM5vS\downloaded_packages'
<U+2714> Package 'questionr' successfully installed.
But, if I launch it just after, it doesn't work 
> library(questionr)
Error in library(questionr) :
no package named 'questionr' is found
It doesn't make any sense... It makes me crazy !