Unable to remove featured image

I tried the codes from this thread https://wordpress.org/support/topic/how-to-remove-featured-image-on-single-posts/

Customize > Additional CSS

Attemp 1:
div.page-header-image-single.grid-container.grid-parent {display: none}

Attemp 2:
add_action( 'after_setup_theme', function() {
remove_action( 'generate_before_content', 'generate_featured_page_header_inside_single', 10 );
} );

Both methods are not working, featured image is still showing on my posts