(The only proper) PDO tutorial: https://phpdelusions.net/pdo/
Organize a php project according to industry best practice: https://github.com/thephpleague/skeleton
PHP Best Practices - A short, practical guide for common and confusing PHP tasks: https://phpbestpractices.org/
Modern PHP Cheat Sheet - A to-the-point summary of all awesome PHP features: https://front-line-php.com/cheat-sheet
Laravel, PHP, JavaScript: https://freek.dev/
PHP security: https://paragonie.com/blog