Hi Sandra,
Thanks for contacting Syncfusion support.
We have checked the reported SfDataGrid not resizing based on the orientation issue in Xamarin.Android but we are not able to reproduce the reported this. SfDataGrid resized properly based on the orientation change. For your reference we have attached the working copy of the sample in the below sample location, please refer it. Could you please do revert us by modifying our sample to replicate the issue. Otherwise please share your SfDataGrid definition code snippet, also please share the details if you use any layout for loading SfDataGrid or share your sample along with replication procedure, that would be more helpful for us to proceed further.
Regards,
Ashok