How to programmatically set a Views display to override style options
This is how you can achieve that:

diff --git a/src/Plugin/views/display/ChartsPluginDisplayChart.php b/src/Plugin/views/display/ChartsPluginDisplayChart.php
index 3dbad31..68048ce 100644
--- a/src/Plugin/views/display/ChartsPluginDisplayChart.php
+++ b/src/Plugin/views/display/ChartsPluginDisplayChart.php
@@ -29,6 +29,10 @@ class ChartsPluginDisplayChart extends Attachment {
     $options['style_plugin']['default'] = 'chart';
     $options['inherit_yaxis'] = ['default' =&gt; '1'];

+    // Set the default style plugin to 'chart'.
+    $options['style']['contains']['type']['default'] = 'chart';
+    $options['defaults']['default']['style'] = FALSE;
+
     return $options;
   }


API docs:
https://api.drupal.org/api/drupal/core%21modules%21views%21src%21Plugin%21views%21display%21DisplayPluginBase.php/function/DisplayPluginBase%3A%3AdefineOptions/8.2.x