After updating to WordPress 5.6 I’m getting the following error while editing Pages in the Admin:
PHP Warning: array_intersect_key(): Expected parameter 1 to be an array, string given in /home/path/to/my/wordpress/install/wp-includes/rest-api/class-wp-rest-server.php on line 1402
I’ve tried deactivating all plugins except for ACF and the error persists. I also tried switching to Twenty Twenty-One and the error still sticks around. Furthermore, once I deactivate ACF, the error disappears.
You should submit bug reports like this here https://www.advancedcustomfields.com/contact/