Hi Claudio,
Thank you for contacting Syncfusion support.
Please use the below namespace in order to access SfAccordion control
Namespace: <Page xmlns:layout="using:Syncfusion.UI.Xaml.Controls.Layout">
We have also prepared a sample by using this namespace.Please download it from the below link
Sample link:
SfAccordionSamplePlease let us know if you need any other assistance
Regards,
M.Sugapriya