Execute shortcodes in feed excerpt

Imagine a shortcode[1] that retrieves a link from a custom field and transforms a word or a phrase into an HTML formatted a element, so for example:

Please, [link]check it out[/link] and let me know.

will be transformed into:

Please, <a href="https://www.ads-software.com">check it out</a> and let me know.

This shortcode works fine in the content and in the feed content, but not in the feed excerpt, which will be outputted as:

Please,  and let me know.

clearing the part inside the shortcode.

Is there a way to tell WordPress to execute this shortcode in feed excerpt? Or, better, how to tell WordPress to execute this shortcode in feed excerpt only if the post has a particular post format (‘link’, for example)?

I make this question because some planets do not retrieve the complete feed content for each post but only the excerpt.

Thanks in advance.
Aldo

[1] The shortcode I am using is this:

add_shortcode( 'link', 'ubn_externalLinks' );

function ubn_externalLinks( $atts, $content = null ) {
	global $wp_query;

	$output = '<a class="external" href="' . htmlspecialchars( get_post_meta( $wp_query->post->ID, 'External_links', true ) ) . '" rel="bookmark">' . $content . '</a>';

	return $output;
}