Hi Eren,
Thanks for contacting Syncfusion support.
We have created simple sample and checked the reported behavior “Unable to change the Text of the Form which is inherited from MetroForm” at our end, we were able to change the text of the MDI child form with desired value. We have attached our sample in which we have tried to reproduce the issue. In this sample, we have added the Test Form to the TabbedMDIManager as Mdi child with modified “Text” value.
If we have misunderstood your query or the above sample doesn’t meet your requirement, please get back to us with more details like sample to reproduce the issue or modify the above sample to replicate the issue at our end. This would help us to provide solution at earliest.
Regards,
Durga S.