Edit wp-includes/class-wp-fatal-error-handler.php and
change this in display_default_error_template( $error, $handled ) (Line: 193):
$message = sprintf(
'<p>%s</p><p><a href="%s">%s</a></p>',
$message,
/* translators: Documentation explaining debugging in WordPress. */
__( 'https://wordpress.org/support/article/debugging-in-wordpress/' ),
__( 'Learn more about debugging in WordPress.' )
);
to
$message = sprintf(
'<p>%s</p><p><a href="%s">%s</a></p>',
$message . ' ' . json_encode($error),
/* translators: Documentation explaining debugging in WordPress. */
__( 'https://wordpress.org/support/article/debugging-in-wordpress/' ),
__( 'Learn more about debugging in WordPress.' )
);
Then preview HTML response to admin-ajax.php using Dev Tools.
