I've checked UI - Battle Menus - (my setting) - Option (#): Ability - Custom Target Menu , nothing is set there.
However it got me thinking and it turns out that UI - Battle Menus - (my setting) - Base Settings - Sub-Menu Settings - Target Box will also override the Use Target menu option. So I guess there are at least these three places that controls whether a target menu will show.
However, even then I remove setting here Sub-Menu Settings - Target Box , the Target menu still exists, just use the default one in UI - Battle Menus - (my setting) - Base Settings - UI Box Settings - UI Box .
Not only that, it seems the Sub-Menu Settings does not always work. For example I set Ability Type Box in Sub-Menu Settings but the ability type menu still uses the default one.
In this video, before 01:10, I showed the target menu still uses the default UI Box UI - Battle Menus - (my setting) - Base Settings - UI Box Settings - UI Box when Battle - Target Setting - Target Selection - Target Menu - Use Target Menu is unchecked.
Start 01:10, setting UI - Battle Menus - (my setting) - Base Settings - Sub-Menu Settings - Ability Type Box has no effect, while ability box uses the default one set in UI - Battle Menus - (my setting) - Base Settings - UI Box Settings - UI Box