By default DDev sites will spam both the CLI and the browser with deprecation warnings. Follow these steps to turn them off. 

1. Make sure the constraint for platformsh/config-reader is ^3.0.
2. .ddev/php/php.custom.ini ("custom" can be whatever you like):
   
   [PHP]
error_reporting = E_ALL & ~E_DEPRECATED & ~E_USER_DEPRECATED
    
3. web/sites/default/settings.local.php
   
   <?php
$config['system.logging']['error_level'] = 'some';
  if (PHP_SAPI === 'cli') {
    error_reporting(E_ALL & ~E_DEPRECATED & ~E_USER_DEPRECATED);
      set_error_handler(function ($severity, $message, $file, $line) {
        if ($severity === E_DEPRECATED || $severity === E_USER_DEPRECATED) {
          return true;
        }
        return false;
      });
}
    
4. .ddev/config.yaml:
   
   web_environment:
  - SYMFONY_DEPRECATIONS_HELPER=disabled
    
5. ddev restart