How to enable bulk selection for theme?

With ?safe_mode=no_plugins no, the menu doesn’t appear. With ?safe_mode=no_themes%2Cno_plugins it does work but that’s obviously just because it disables 3rd party themes.

I downloaded the main branch from GitHub - discourse/discourse-simple-theme: Sam's simple discourse theme · GitHub and a quick search for bulk in all the files doesn’t find anything.