How to retrieve Post Excerpt from a different site in the Network

Yes, using switch_to_blog() you can load another WordPress site, get what you want, then revert back to your current site and carry forward any retrieved data.

// the different site ID in your WordPress Network
$otherSite = 3;

// the post excerpt you're after in the different site
$otherSitesPost = 42;


switch_to_blog( $othersite );

$otherSitesPostExcerpt = get_post($otherSitesPost)->post_excerpt;

restore_current_blog();

echo "Site #{$otherSite} post #{$otherSitesPost} excerpt: {$otherSitesPostExcerpt}";