Ubuntu 20.04

Install XDebug
https://xdebug.org/docs/install

PHP Debug Adapter for Visual Studio Code
https://marketplace.visualstudio.com/items?itemName=felixfbecker.php-debug

$ cd /etc/php/7.4/mods-available

$ gedit xdebug.ini

zend_extension=xdebug.so
xdebug.remote_enable=1
xdebug.remote_autostart=1

$ phpenmod xdebug

$ sudo service apache2 start

In Visual Studio Code, launch.json

{

    "version": "0.2.0",

    "configurations": [

        {

            "name": "Listen for XDebug",

            "type": "php",

            "request": "launch",

            "port": 9000

        },

        {

            "name": "Launch currently open script",

            "type": "php",

            "request": "launch",

            "program": "${file}",

            "cwd": "${fileDirname}",

            "port": 9000,

            "runtimeExecutable": "/usr/bin/php"

        }

    ]

}