Hello everyone,
My "Documents" folder is missing from dolphin and from my hdd. In system settings, in "Location for Personal Files", the documents folder path is set to my homedir.
When I type "xdg-user-dirs-update" in a terminal I got :
"/home/<username>/Documents was removed, reassigning DOCUMENTS to homedir."
I didn't remove them by mistake, I checked bash history.
It is likely to be because of updates. I did the standard "apt update", "apt dist-upgrade". The updates were pretty big and was mainly libs and linux-image. Could the updates be the cause ?

I'm running Debian 10 buster, Dolphin 18.08.0, KDE 5.54.0 and Plasma 5.14.5.

in a konsole, can you go to the folder? If not, then you must have removed it inadvertently. If you haven't written on the disk since this happened, it should be recoverable from the Trash folder.

It is very highly unlikely that any update and upgrade action did remove this, as it is a standard folder in a users home.