Help with D8 .theme preprocessing and field manipulation

My head is stuck in D7, can someone assist in how I need to manipulate field values in preprocessing for D8?
Here is where I am now. It semi-works as in I am getting at the field value I need to drop into a var for twig, but I cant figure out how to remove/unset the field so it wont render.
Also I am fairly sure there this is the wrong (long) way of manipulating field values (can someone put me on the right path?) Any assistance greatly appreciated!!!!

function myTheme_preprocess_block(&$variables) {

	 $viewMachineName = $variables['elements']['content']['#display_id'];

	 if ($viewMachineName == 'block_my_view_machineName') {
		 
                 // get node field
                 $sidebarTitleField = $variables['elements']['content']['#view']->result[0]->_entity->get('field_sidebar_callout_title')->getValue();

		 // set var to be used in twig (would rather update object so this field value drops into the blocks title if I knew how)
                  $variables['blockLabel'] = $sidebarTitleField [0]['value'];

                 // remove field so it wont render  (but doesn't work)
		 $variables['elements']['content']['#view']->result[0]->_entity->__unset('field_sidebar_callout_title');

	 }

}