Hi Jarek,
We have prepared the sample for CustomPrintPreview using UserControl in SfDataGrid, you can download it from below mentioned location.
We already have an sample in our dashboard for CustomPrintPreview, you can get it from below mentioned location.
Path Location: \{installed location}\Users \{Users.Login}\AppData\Local\Syncfusion\EssentialStudio\{installed Syncfusion ES build version}\WPF\SfGrid.WPF\Samples\CustomPrintPreview
Please refer the below User Guide documentation for more details.
If provided solution does not meet your requirement kindly share more details about your requirement that will be more helpful to provide appropriate solution at the earliest.
Regards,
Gnanasownthari T.