https://learn.microsoft.com/ru-ru/dotnet/api/system.windows.forms.combobox.endupdate?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-10.0
ComboBox.EndUpdate Method (System.Windows.Forms) | Microsoft Learn
Resumes painting the ComboBox control after painting is suspended by the BeginUpdate() method.
windows formscomboboxmethodsystemmicrosoft