Hello Andrej,
In the debug log I see the following
export_file: csv, this is the reason why you get a CSV file. This is supposed to be XML by default and I have no idea how you managed that

The only thing I can think of is that you changed the template type while building the template.
What you can try to do is the following and follow the steps exactly:
- On the Details tab set the Operation to Product
- Click on Save
- On the File tab set Export type to XML
- On the Details tab set the Operation to Google Merchant
- Click on Save
- Run your export
Let us know how it goes.
Kind regards,
RolandD
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