Install PHP 8.0 Yaml extension on Ubuntu 18.04

I wrote a simple php based on the fisrt example.

php.net/manual/es/function.yaml-parse.php

I got...

I use ondrej repository to install php.

There is no package to install yaml extension.

Ok, let's try to compile it with phpize.

There is not phpize either or php8.0-dev (In debian phpize ussualy is there)

I tried with Ubuntu 22.04 too. The ondrej have no php8.x-dev php8.x-yaml. And php-dev o php-yaml try to install php7.2 versions.

Besides, ymal code on PECL requires php 7.

What would be the proper way to install it in these circumstances?

I have used github.com/dallgoot/yaml to solve it, but I have curiosity with this issue.