As per:
https://www.kreationsbyran.se/php-debugging-in-vscode-with-xdebug-and-mamp/
the key is to install PHP-Debug extension in Visual Studio Code, configure MAMP to use Xdebug. Let VSCode create a .vscode/launch.json file automatically and start your debugging session. Depending on the version of VSCode the button in the debugger window may be labeled differently or placed elsewhere.
It just works.