Keep sidebars in sections

Hi, I searched on the forum for the answer to this, trying to use sections in my homepage, while keeping the sidebars, and saw that it was recommended to add this filter:

add_filter( 'generate_sections_sidebars','__return_true' );

However, when I go to the customize and additional CSS section, I get an error code "unexpected token at....".

I don't have a lot of coding experience, trying to get this solved in the easiest possible way.

Thank you!