Again, for logstash this is just a pass-through to MaxMind. If their library can handle .dat then it will work, if not, it will not. It is not a logstash question, it is a MaxMind question.
The plugin is a Logstash plugin installed with the application having official documentation. Users don't really care how it's solved under the hood. It's fine if you don't know the answer for the question, as I mentioned before, those who asked this before, didn't got any answer either.
Also, the ".dat" format is the legacy GeoLite format so one would think it's supported. However, it looks like LS stopped supporting it and needs "mmdb" while -for example- Nginx supports that one.
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