Enable Dynamic Data Sources

We want to use Power BI to analyze and manage our data. To do this, we need to get data from a list of data sources. The data is processed according to the same scheme. That is why we have implemented a Custom function with which the data is fetched from a data source and then processed. This works fine in Power BI Desktop. The first problem was that the queries in the Power BI Service could not be put together because the data sources build on each other. To this day we do not know why this has to be the case. Now that we had user access to Power BI premium today, we could have solved this problem with a combination of data flows. However, it was not possible to save the data flow with our custom function. Reason: Dynamic Data Sources are not allowed. I don't know how other companies with these restrictions can manage their ETL in Power BI. For us, this means that we cannot use Power BI for ETL Jobs.