Unfortunately, RadPropertyGrid does not provide such functionality out of the box as it is pretty specific. You can consider the approach from the other thread that you have checked with manually defining the PropertyDefinitions, however, since in your exact scenario you are not aware of the structure of the control it will not be very straightforward to achieve.You can check the Customized Property Definitions
article for more information.
I also advise on checking the "Nested Properties" demo regarding the PropertyGrid control in our WPF Demos Application
and consider such approach at your end. I am not familiar with the exact structure аt your end but it seems similar to your requirement.
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and share your thoughts.