There are a few options you can turn on to help you on your DataGrid object
EnableColumnVirtualization = true
EnableRowVirtualization = true
These two are the main ones I think might help. Next try making your binding async
ItemsSource="{Binding MyStuff, IsAsync=True}"
And lastly, I’ve heard that setting a maximum height and width can help even if it above the max screen size, but I didn’t notice a difference myself (claim had to do with auto size measuring)
MaxWidth="2560"
MaxHeight="1600"
Also never put a DataGrid in a ScrollViewer, because you will essentially lose virtualization. Let me know if this helps!