If you are in edit mode using InCell, clicking somewhere else inside or outside the Grid should fire OnUpdate if the item is valid. However, if you click on some customly added element in the Grid (e.g. button, icon, dropdown) this will not fire OnUpdate for a valid item.
In Incell edit, clicking anywhere besides the edited cell should fire OnUpdate for a valid input.
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ADMIN EDIT
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A possible workaround for the time being - in the OnClick handler of the custom element get the edited item from the Grid State. Update the item and programmatically close the edit mode.
For example: https://blazorrepl.telerik.com/ccuMGovv08NIX6u544.