In GA4, Google replaced the Multi-Channel Funnels Reporting API with the Google Analytics Data API, having made significant changes to the data model, analyses, and metrics. However, as of now, the GA4 Data API doesn’t offer a direct substitute feature to pull up the assisted conversion paths data like the old Multi-Channel Funnels Reporting API. GA4 only notably supports analyses based on the “first user source” and “session source” which somewhat limit the view of the conversion path. While you wait for Google to potentially roll out a feature for assisted conversion, you may indeed need to devise a new method to generate similar data. You might do so by piecing together user journeys from the user engagement data, but this can be complex and might not fully match the old assisted conversion paths metric.