I installed the new Contact Layout Editor extension, but I am not finding the new menu item, which should be at Administer / Customize Data and Screens.
Joomla 3.8.12 Civi 5.5.1
(Aside: in this process, I discovered that the extension created a new SQL table as MyISAM, which threw a warning in Civi. Easy enough to change the table to InnoDB, but it seems like a new extension should be using InnoDB by default. See https://github.com/civicrm/org.civicrm.contactlayout/issues/14. Fixing the engine did not solve the problem of the missing menu.)