Depending on what saved objects you're looking at, it will be very difficult to compare them. Each saved object type has its own unique attributes that are stored. Unfortunately there's no easy answer to compare/contrast two different saved objects. Manually looking at the difference in the JSON is the only way to really do this.
If you're looking to ensure that certain aspects of your environments are the same, you can use the Saved Objects Management page to export saved objects from one environment and import them into another environment. It sounds like you already exported objects seeing as you have an .ndjson file. Note that this will only affect Kibana's saved objects, it will not affect any other data in your Elasticsearch cluster. You can use Elasticsearch snapshots if you want to copy data from one Elasticsearch cluster to another.
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