How to get field value after getting a node?
If you want to use node object from entityTypeManager, you need to get current value from the array after loading like below:

$schoolNode = \Drupal::entityTypeManager()
      -&gt;getStorage('node')
      -&gt;loadByProperties(['field_school_id' =&gt; $item['schoolId']]);
$node_load = current($schoolNode);
$schoolname = $node_load-&gt;field_school_name-&gt;getValue();


This is only for a single node. If you have multiple nodes, foreach node as

foreach(schoolNode as $node){
  $schoolname = $node-&gt;field_school_name-&gt;getValue();
}