Yaml files use colons instead of equal signs, and no semi-colons at the end. Try this:
index.max_result_window: 5000000
Do note that the setting is there for a reason. It protects your cluster from abusively large search requests. 5,000,000 is certainly an abusively large request and will likely hurt the performance of your cluster, potentially even crashing it.
If you need large result sets, you should scan scroll over the data instead.
[WARN ][o.e.b.ElasticsearchUncaughtExceptionHandler] uncaught exception in thread [main]
org.elasticsearch.bootstrap.StartupException: java.lang.IllegalArgumentException: node settings must not contain any index level settings
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