LibAddonMenu is LAM. The description is for development as it is a library, not an addon!
https://www.esoui.com/downloads/info7-LibAddonMenu.html
You need to install addons which use LibAddonMenu-2.0 as dependency. These addons create addon settings menus via the Library LibAddonMenu.
LibAddonMenu installed alone does nothing on its own!
What addon told you to install LAM? This needs to call the library and you'll see the settings menu then
If you enable LAM and this addon ingame in the addon manager.
You can also use Votans Addon List to automatically enable/disable dependencies for your addons.
You just need to install the dependencies via Minion (like LibAddonMenu, LibCustomMenu, Lib...)