Adding Steam libraries on Linux

About

Sometimes Steam decides it no longer wants to use a library despite having started up with it present many times prior due to any number of buggy behaviours leaving everything saying "Install" Instead of "Play".

In my experience with the modern Steam UI this year it also refuses to display any options at all under the Settings > Storage > Add Drive > "Create or select new Steam library folder" dialogue anymore either making it seemingly impossible to re-add the library.

Solution / Workaround

With this problem not going away any time soon with many threads of many hit or miss suggestions out there I've had better luck using the modern Steam UI's hidden Console tab to restore dropped libraries in an instant.

Commands

This console feature can be accessed by either starting steam with the argument to enable it and going to the tab or more easily just visiting the steam browser protocol address on demand: steam://open/console to be bought to the tab immediately.

From the Console tab in Steam's main window you can then issue the library_folder_add command to restore your external library. In my case this was library_folder_add /data/steam. And just like that my Library tab had all my titles ready to use.