how to create custom Variable for Schema, such as autor Profile Picture

Hello,

Thank you for contacting Rank Math support today.

Please refer to this code here to create a custom variable and use the shortcode %shortcode_var_name%:

add_action( 'rank_math/vars/register_extra_replacements', function(){
	rank_math_register_var_replacement(
	   'shortcode_var_name', [
	   'name'        => esc_html__( 'VAR name', 'rank-math' ),
	   'description' => esc_html__( 'VAR description', 'rank-math' ),
	   'variable'    => 'shortcode_var_name',
	   'example'     => shortcode_var_name_call_back(),
	   ],
	   'shortcode_var_name_call_back'
   );
});
function shortcode_var_name_call_back(){
	return "Value";
}

You may refer more here: https://rankmath.com/kb/filters-hooks-api-developer/

Hope that helps and please do not hesitate to let us know if you need our assistance with anything else.