https://www.syncfusion.com/feedback/33631/need-to-provide-dropdownwidth-support-in-sfcombobox
Need to provide DropDownWidth support in SfComboBox in WinForms | Feedback Portal
Check out the feature request in WinForms - SfComboBox - Need to provide DropDownWidth support in SfComboBox.
needprovidesupportwinformsfeedback