Template Style field not shown in Menu Items
From Joomla! Documentation
Errors reported[edit]
The template style field does not display when editing or creating a menu item.
Version affected[edit]
General Information
This pertains only to Joomla! version: 3.9.2
What is the cause[edit]
Wrong showon in item.xml
This is a bug introduced in Joomla! 3.9.2.
How to fix[edit]
Apply this Patch or wait for Joomla! 3.9.3.
Replace in administrator/components/com_menus/models/forms/item.xml line 149
showon="params.alias_redirect:0"by
showon="type!:alias[OR]params.alias_redirect:0"