Determine whether current page does not render the theme outputs

Hi there,

I’m wondering what would be a good way to detect whether the current page is loaded in the background which does not involve theme rendering.

At the moment, I’m doing something like this,

if ( in_array( $GLOBALS[ 'pagenow' ], array( 'wp-cron.php', 'admin-ajax.php' ) ) ) {
    // yes
} else {
    // no
}

But there must be other pages that do not render the theme outputs like the REST API and feeds, possible more which I’m not aware of. Does anybody know a good way to do it?