I want to incorporate multiple Lambda functions into my workflow and find a way to extract and stream the raw logs from each function to Splunk, from my understanding, Execution Log Streaming comes with a predefined base schema, and I cannot integrate my own Lambda functions log into it.
That is correct about Workflows Execution Log Streaming. It uses a fixed schema that cannot be changed by the end user. This feature is currently in EA, and can be enabled for testing by going to Settings >> Features in the Okta admin console.