HiBill Rahe,
Thank you for reaching out to us.
To dynamically enable or disable a component, you can make use of the Enabled property. Additionally, to disable specific items within the component, you can use the ComboBoxFieldSettings.Disabled property by setting it to true or false accordingly.
Please refer to the following documentation and demo links for more details:
ComboBox
DropDownList
If you are looking to implement cascading dropdown functionality, please refer to the resources below:
ComboBox - Cascading
DropDownList - Cascading
For your convenience, here is the link to the Syncfusion Blazor documentation overview as well.
Please let us know if you need any further assistance.
Regards,
Priyanka K