Write below code in current WordPress themes in function.php
/wp-content/themes/twentytwenty/functions.php
/* Disable Automatic Updates in WordPress */
function remove_core_updates(){
global $wp_version;return(object) array('last_checked'=> time(),'version_checked'=> $wp_version,);
}
add_filter('pre_site_transient_update_core','remove_core_updates');
add_filter('pre_site_transient_update_plugins','remove_core_updates');
add_filter('pre_site_transient_update_themes','remove_core_updates');
/* .Disable Automatic Updates in WordPress */
