Cannot disable theme picker in UI16
The process to disable the theme picker (described in the product documentation at https://docs.servicenow.com/administer/navigation_and_ui/task/t_EnableTheThemePicker.html) does not work in UI16, although it does work in UI15 and UI11. The two UI macros of ui_theme_changer exist because one is for UI15 and the other is for UI11; however, they are not used in UI16.
Steps to Reproduce
In an instance running UI16, navigate to System UI > UI Macros.
Find and select the ui_theme_changer UI macro.
Deselect the Active field and click Update.
Despite this setting, the theme picker is still active.
To prevent users from changing their themes:
Access all the themes available for UI16 (Concourse) by going to http://<instance name>/sys_ui_theme_list.do?sysparm_query=device%3Dconcourse.
Set all of the themes to active = false.
Related Problem: PRB658866