Error upgrading Magento 2.3.5-p1 to 2.4.0

Cloudways support came back quickly for them, although the answer wasn’t overly helpful:

Hello there,

Could you please confirm the developer of the application. In order to make sure the ioncube is not required on it. As only the developer of the site can confirm these details. As on the PHP7.4 the iconcube is not available on it.

Please let us know if you require any further information from our side.

Thank you.

Regards

As I have a backup/restore facility within Cloudways, I went ahead and upgraded PHP to 7.4. Now I get this error when running composer update:

  Problem 1
    - magento/magento-coding-standard 1.0.2 requires squizlabs/php_codesniffer ~3.3.0 -> satisfiable by squizlabs/php_codesniffer[3.3.0, 3.3.1, 3.3.2] but these conflict with your requirements or minimum-stability.
    - magento/magento-coding-standard 1.0.1 requires squizlabs/php_codesniffer ~3.3.0 -> satisfiable by squizlabs/php_codesniffer[3.3.0, 3.3.1, 3.3.2] but these conflict with your requirements or minimum-stability.
    - magento/magento-coding-standard 1.0.0 requires squizlabs/php_codesniffer ~3.3.0 -> satisfiable by squizlabs/php_codesniffer[3.3.0, 3.3.1, 3.3.2] but these conflict with your requirements or minimum-stability.
    - magento/magento-coding-standard 1.0.2 requires squizlabs/php_codesniffer ~3.3.0 -> satisfiable by squizlabs/php_codesniffer[3.3.0, 3.3.1, 3.3.2] but these conflict with your requirements or minimum-stability.
    - Installation request for magento/magento-coding-standard ~1.0.0 -> satisfiable by magento/magento-coding-standard[1.0.0, 1.0.1, 1.0.2].

I’ve set php_codesniffer manually in composer.json

"squizlabs/php_codesniffer": "~3.5.4"

Now what is the issue?