Next step I would take is to find out which version of PHP Apache is running. It’s possible Apache runs a different version than the cli version you’re using when you run php -v. One kind of hacky method is to temporarily rename the .htaccess file in the web root, then create a file there called phpinfo.php with the following contents, then in the browser go to your nextcloud domain and add /phpinfo.php to the end (for example cloud.yourdomain.com/phpinfo.php):
<?php
phpinfo();
?>
If you do this, please don’t forget to delete the phpinfo file and also restore .htaccess so you don’t leave your instance open to attacks.
You might just need to disable the old php module and enable the new one for Apache as described here: https://serverfault.com/questions/707383/installed-new-version-of-php-but-apache-still-using-the-old-version
Basically (assuming the old version of PHP you had was 7.3):
sudo a2dismod php7.3
sudo a2enmod php7.4