Thanks for the additional context @95784285 .
There isn't a built-in indexer for Azure Data Explorer since the underlying Kusto clusters aren't supported data sources. What you would have to do is create your own indexer leveraging an Azure Function or Logic app that queries that data sources you want searched and use the Push API to the index, see Data import in Azure Cognitive Search.
Another option is Copy data to an Azure Cognitive Search index using Azure Data Factory or Synapse Analytics where you utilize a sink to push the data your index. However, going this route doesn't support complex types. You can also try an intermediate sink to storage account and use Index data from Azure Blob Storage.