Situation: linking/appending multiple folders from a *.blend subfolder using the mouse and keyboard modifiers is impossible.
Right now, per a report on discord, you can't fill select, nor multiselect very easily. In the BFA keymap, it's impossible unless you use CTRL+SHIFT for a fill/extend select, which is inconsistent with the outliner behaviour - and ultimately broken.
This means the experience to append/link data is broken, and inconsistent right now.
Go through the Blender keymap and make the BFA hotkeys consistent in the filebrowser, just like in Outliner Main hotkeys similar or consistent with how the outliner should work in the BFA keymap.
Hotkeys to resolve:

L Click = turn off "open"and turn on "Deselect on Nothing"
_This fixes the the ability to select folders, instead of opening them, and allows to remove a hotkey to deselect things._
Shift + L click = turn off "open"
_This allows to select multiple folders without going into them immediately_
Change SHIFT + CTRL + L click = change to only CTRL + L click, then this can be either removed, and/or turn off "open". Change CTRL + L Click to F2.
_Reason is, this is a double hotkey WITH a mouse, which is ok, but not really ideal. An alternative for this entry is just CTRL+L click like in the outliner, then change the Rename Folder/File to F2 to make it consistent with OS standards. Make sure the "open" is off._


So you mean we should fix the Blender keymap to work like in Bforartists and not like in Blender?
The Bforartists one is broken. Blenders one is working better here.
EDIT: fixed up the english a bit.
Ah okay :)
Hm, Blender does not have Shift Ctrl Left Mouse. And we don't have double left mouse for select. Plus a few more inconsistencies.
I will try to implement the Blender keymap here now ...
Left a few hotkeys away. F2 is still under discussion for example. And a extra hotkey for refresh makes no sense when the refresh button is top UI anyways. But the keymap is now consistent against the Blender keymap.
Now let's fix the manual ...
Manual updated here: https://github.com/Bforartists/Manual/commit/2253188a473a001d3391563744b374d069359de6
Closing. Fixed in master. And thanks for the report :)