What is the way to add there some document manually?
(E.g. to put a
*.desktop file into some specific folder, or to run some command similar to
xdg-open, or etc.)
You could enter
find ~ \( -type d -or -type f \) -iname '*recent*' to get a list of files and directories that contain
RECENT, or some other case permutation thereof, in their names that exist in your home directory --
-iname means case insensitive name. Then, it would be a matter of inspecting the results one by one.
In my case (Debian Testing), it's in