Are you sure you want to be using the cutting edge nightly releases (I spotted that with the reported version 5.99.0)? The nightlies might have the “latest” features, but there is no guarantee that those features actually work or don’t break other parts. Before you get too far, you might want to run the latest stable version, 5.1.4 as the latest nightlies (can? will?) create projects that aren’t readable by the latest stable version.
That said, regarding your specific question, just configuring the path for where the libraries isn’t enough. You need to also specify which libraries in that location you want to use. Here are some FAQs for you to peruse to help you get a grasp on library management. (I threw in one specifically for Linux, but I don’t use Linux so I’m not sure if it applies to your situation.)
- Library management in KiCad version 5
- I had KiCad 4 installed previosly. Now i updated to v5. Now i have some problems with the library setup
- Where are the configuration files (settings, library tables)?
- Creating a new symbol library and a new symbol in KiCad 5
- I installed KiCad 5 (under Linux) but there are no libraries. (The default option for sym lib table setup is disabled)
Those FAQ entries and many others can be found when you click the FAQ link in the header bar for the forum (just to the left of the search icon). The top, pinned entry in that area includes a categorized index to help you find the correct entry.
Or, are you reporting a new bug in the latest nightlies to get fixed? If so, the proper place to report those bugs are over on Launchpad.