Hi Techlandandyzhang,
Greetings from Syncfusion support.
We have checked the reported issue with shared sample code. In the sample, you have written code for restricting the special characters. If you are typing restricted characters in the English keyboard, Syncfusion TextBox prevents the value typing correctly.
When you are enabled the Microsoft PinYin mode for input, then the restricted characters are allowed both in the Syncfusion TextBox component and HTML 5 Textbox component. Since, the Chinese characters are differed from the English characters. So, we suggest you to make the condition based on the Chinese keyboard in the application itself to get rid of the reported issue.
Regards,
Berly B.C