Greetings from Syncfusion.
Currently, we do not have support for RotationAngleChanged event on SfRadialMenu. So, we have considered your request as a feature and logged a feature report. This can be tracked through our Feedback portal using the below link.
Please cast your vote to make it count. We will prioritize the features every release based on the demands.
If you have any more specification/suggestions to the feature request, you can add it as a comment in the portal.