General developer forum

Hi,

I have encountered the same problem and I found the following solution

Before going further, check this out
https://docs.moodle.org/dev/Boost_Navigation

Excerpt:
"These navigation elements are custom elements that only exist in the boost theme. The boost theme has it's own core renderer which is where they are defined. See theme/boost/classes/output/core_renderer.php. The functions are region_main_settings_menu() and context_header_settings_menu()."

Based on my understanding, the method region_main_settings_menu() can only be found in the boost core renderer. Hence, when trying to override the core renderer, instead of using

class theme_mytheme_core_renderer extends core_renderer 

you have to use

class theme_mytheme_core_renderer extends theme_boost\output\core_renderer 

to point exactly to the boost core renderer.

Having done that, the error is gone.

Hope it helps.

Thanks

Rafiq