Unfortunately, ADF does not support true event-based triggers for SFTP.
ADF event triggers only work with Azure Blob Storage, Azure Data Lake Storage Gen2 and Azure Event Grid-integrated services. Because SFTP does not emit events that ADF can consume.
To simulate event-based triggering for SFTP file availability, a robust and Azure-native workaround is to use Azure Blob Storage as an intermediary layer. This allows you to leverage native Blob-created events to trigger your ADF pipeline, only when a file is detected.
For connecting SFTP server in BLOB, kindly refer - SFTP support for Azure Blob Storage
We can create Event based trigger, now as the file appears in BLOB so this will trigger the pipeline as soon as new file will appear in the BLOB. For creating event based triggers in ADF, kindly refer - Creating a trigger that runs a pipeline in response to a storage event