I recommend you to access your website directory via FTP, and in the /wp-content/plugins/ folder, find jetpack folder. You can delete or just rename that folder.

Ater that, go back and try to access your wp-admin dashboard. If all things are fine now, then it is a compatibility problem in your site.

You can deactivate all your plugins and activate one by one, to find which one of them is causing this mistake.

Let me know if this solves your problem or not.