Error after last wordpress update

Hi, today we updated to wordpress last version and got this error (we use PHP 7.3):

WP RSS Aggregator has encountered a critical error. The safest course of action is to deactivate the plugin and any of its add-ons on this site using the button below. Once you’ve done that, you may reactivate them and start using the plugins again. If the problem persists, please copy the below error and send it to our support team with an explanation of when and how it happened.

Error Message:
Call to undefined function Symfony\Polyfill\Mbstring\iconv() (wp-content/plugins/wp-rss-aggregator/vendor/symfony/polyfill-mbstring/Mbstring.php:409)
Stack trace:
#0 /home/XXXXXXX/public_html/wp-content/plugins/wp-rss-aggregator/vendor/symfony/polyfill-mbstring/bootstrap.php(45): Symfony\Polyfill\Mbstring\Mbstring::mb_check_encoding('a:19:{s:31:"ad-...', 'ASCII')
#1 /home/XXXXXXX/public_html/wp-includes/wp-db.php(3006): mb_check_encoding('a:19:{s:31:"ad-...', 'ASCII')
#2 /home/XXXXXXXX/public_html/wp-includes/wp-db.php(3117): wpdb->check_ascii('a:19:{s:31:"ad-...')
#3 /home/XXXXXXXX/public_html/wp-includes/wp-db.php(2452): wpdb->strip_invalid_text(Array)
#4 /home/XXXXXXXXX/public_html/wp-includes/wp-db.php(2323): wpdb->process_fields('XXXXXXXXX_option...', Array, NULL)
#5 /home/XXXXXXXXX/public_html/wp-includes/option.php(441): wpdb->update('XXXXXXXXX_option...', Array, Array)
#6 /home/XXXXXXXXX/public_html/wp-content/plugins/jetpack/vendor/automattic/jetpack-sync/src/modules/class-callables.php(421): update_option('jetpack_plugin_...', Array)
#7 /home/XXXXXXXXX/public_html/wp-includes/class-wp-hook.php(292): Automattic\Jetpack\Sync\Modules\Callables->set_plugin_action_links(Object(WP_Screen))
#8 /home/XXXXXXXXX/public_html/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters(NULL, Array)
#9 /home/XXXXXXXXX/public_html/wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#10 /home/XXXXXXXXX/public_html/wp-admin/includes/class-wp-screen.php(421): do_action('current_screen', Object(WP_Screen))
#11 /home/XXXXXXXXX/public_html/wp-admin/includes/screen.php(240): WP_Screen->set_current_screen()
#12 /home/XXXXXXXXX/public_html/wp-admin/admin.php(212): set_current_screen()
#13 /home/XXXXXXXXX/public_html/wp-admin/plugins.php(10): require_once('/home/XXXXXXXXX/...')
#14 {main}

We disabled and re-enabled the plugin and didn´t fix the situation.

Could you help us please?