As simple as this: if you don’t believe in solutions with Dataflow and just copy queries across most likely you are going to get the following error:
I had multiple data sources: Dataverse and CSV file. Because I didn’t go through the normal order for steps but just started with an empty query and just copied queries across I started getting this error immediately after adding a Dataverse query.
You may get this error for different issue but in this case it’s not what it seems. To fix the issue you have to go to Project options and tick to allow combining data from multiple sources. Of course, you have to make sure you follow your data policies.
In my case, all data belong to one organisation and it’s queried for the internal purpose.
This fixed the issue.
If you do it in a normal way, just by adding steps to the script, it asks you when you are trying to add another source. In this case it just “screams” in its own way.