PHP 7.4 was officially released at the end of November last year, bringing a lot of useful new features, such as FFI that can be used to access C structures/functions/variables in native PHP code, Opcache preloading, simplified anonymous functions, and type attributes support and more …
What’s more important is that compared to providing PHP 7.3, PHP 7.4 can get an extra year of technical support from the PHP development team. Given that Ubuntu 20.04 is a long-term support release and will be deployed on a large scale in servers and cloud services, there is no reason not to introduce PHP 7.4 into Ubuntu 20.04.
In addition to functional improvements, PHP 7.4 has performance advantages. Especially for users using Ubuntu 18.04 LTS, upgrading to Ubuntu 20.04 should obviously notice the speed increase of PHP workload.
If users currently using Ubuntu 18.04 are upgrading to 20.04, please note that their PHP version will also be upgraded from 7.3 to 7.4, so you should also refer to the migration guide for upgrading from 7.2 to 7.3. Also note that phpunit has also transitioned from 7.5.6 to 8.5.2, which changed the behavior of features used in some test cases.