The extended DDL is reopened as soon as it is clicked to close it. The problem can be reproduced on Telerik's demo page. Blazor UI version 3.6.1 and 4.0.0 on Safari 15.6.1 and 16: https://docs.telerik.com/blazor-ui/components/combobox/overview#creating-combobox

An open ComboBox will not close when the user tabs out of it when the ComboBox is the last component on the page. Here is a test example: Creating Blazor ComboBox

If there is another component after the ComboBo, then tabbing out works correctly.