When i edit a page an error message appears, if i deactivate the plugin its ok

Hi there,

The following error message appears:


Fehler-Details

==============

Ein Fehler vom Typ E_ERROR wurde in der Zeile 4169 der Datei /volume1/web/wordpress/wp-content/plugins/options-for-twenty-twenty-one/options-for-twenty-twenty-one.php verursacht. Fehlermeldung: Uncaught Error: Class 'WpOrg\Requests\Utility\CaseInsensitiveDictionary' not found in /volume1/web/wordpress/wp-content/plugins/options-for-twenty-twenty-one/options-for-twenty-twenty-one.php:4169

Stack trace:

#0 /volume1/web/wordpress/wp-includes/class-wp-hook.php(292): options_for_twenty_twenty_one_class->oftto_pre_http_request(false, Array, 'https://options...')

#1 /volume1/web/wordpress/wp-includes/plugin.php(212): WP_Hook->apply_filters(false, Array)

#2 /volume1/web/wordpress/wp-includes/class-http.php(257): apply_filters('pre_http_reques...', false, Array, 'https://options...')

#3 /volume1/web/wordpress/wp-includes/class-http.php(626): WP_Http->request('https://options...', Array)

#4 /volume1/web/wordpress/wp-includes/http.php(162): WP_Http->get('https://options...', Array)

#5 /volume1/web/wordpress/wp-admin/edit-form-blocks.php(203): wp_remote_get('https://options...')

#6 /volume1/web/wordpress/wp-admin/post.php(187): require('/volume1/web/wo...')

#7 {main}

  thrown

It is a page that is not publicly accessible, so I cannot post the link publicly. The site is hosted on a Synology NAS.

can anyone help?
Thank you in advance

Hans