ContentPage is not a Telerik UI for MAUI control, you can ask this question on StackOverflow or Microsoft Q&A to get an answer.
I have noticed you opened four other posts that are completely unrelated. The Telerik Forums are for questions of problems focused on using the Telerik controls, not general .NET or MAUI programming questions.
To get help for .NET MAUI programming questions, you will want to ask those question in the place where you can get assistance for them. The links I provided above are where you can get further assistance.
Regards,
Lance | Manager Technical Support
Progress Telerik