Hi Mark Tannehill,
Good day to you.
We have checked your provided image and reported problem at our end. We suspect that, you are expecting the filtering functionality in DropdownList component. For this scenario, you can follow the below help document to achieve your requirement.
If we misunderstand your requirement, then please revert us with the detailed explanation for your requirement along with below details.
a. Component details
b. Code block of your problem
c. Syncfusion Package version
Regards,
Ashokkumar B.