fatal error | WordPress.org

Hi all,
I let my website update several plugins recently, and since that moment I can not access anymore.
The error message is the following one:

Fatal error: Cannot redeclare add_option_whitelist() (previously declared in /home/users6/l/lmv2512/www/wordpress/wordpress/wp-includes/deprecated.php:4079) in /home/users6/l/lmv2512/www/wordpress/wordpress/wp-admin/includes/plugin.php on line 2180

I am quite a basic user of wordpress and I don’t really know how to fix that. Does anyone has an idea, to fix it (simply)?
Thanks a lot!

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