WordPress Multisite, gets all site transient keys in the database with a specific prefix.

example.php

<?php

foreach ( get_site_transient_keys_with_prefix( 'my_tranients_prefix_' ) as $transient ) {
	delete_site_transient( $transient );
}

get_site_transient_keys_with_prefix.php

<?php
/**
 * Gets all site transient keys in the database with a specific prefix.
 *
 * Note that this doesn't work for sites that use a persistent object
 * cache, since in that case, transients are stored in memory.
 *
 * Inspired by: https://kellenmace.com/delete-transients-with-prefix-in-wordpress/
 *
 * @param  string $prefix Prefix to search for.
 * @return array          Transient keys with prefix, or empty array on error.
 */
function get_site_transient_keys_with_prefix( $prefix ) {
	global $wpdb;

	$network_id = get_current_network_id();
	$keys       = $wpdb->get_results(
			$wpdb->prepare(
			"SELECT meta_value, meta_key FROM {$wpdb->sitemeta}
	      		 WHERE meta_key LIKE %s AND site_id = %s",
			$wpdb->esc_like( '_site_transient_' . $prefix ) . '%',
			$network_id
		),
		ARRAY_A
	);

	if ( is_wp_error( $keys ) ) {
		return [];
	}

	return array_map(
		function( $key ) {
			// Remove '_site_transient_' from the option name.
			return str_replace( '_site_transient_', '', $key['meta_key'] );
		},
		$keys
	);
}