emacs doesn't displays Rd files content in package development

Question

I make R package development in emacs by the help of the devtools (and roxygen2) package to create Rd files and display them by ?function_name. Normal workflow:

• write functions in R files
• call devtools::load_all() and devtools::document()
• call ?function_name to display formatted Rd content

Rd files are created. NAMESPACE is updated. With my old system in emacs and with the new system in a shell the formatted Rd content is displayd. But if I do the same in my new system in emacs I get now the error message:

Can’t find documentation for ‘function_name‘

Any hints to fix the problem?

My new system:

• MX-Linux 21.2.1 KDE_x64 Wildflower
• emacs 27.1
• ess 18.10.3snapshot (ess-20220915.2126 installed over elpa)
• devtools 2.4.4
• roxygen2 7.2.1