Internally dates are stored in UTC. When date format contains a timezone Elasticsearch uses it to convert to UTC, but without a timezone it just assumes UTC.
I think you'll have to convert to a UTC timezone or specify your timezone during ingestion, as it won't be possible to fix on index mapping level.
Regarding Kibana advanced setting: this is just a UI formatting configuration. With it you can specify how you want to display dates in Kibana that are stored in UTC in Elasticsearch
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