[EuiComboBox] Remove dropdown arrow when disabled; [EuiSelect] Remove Chrome opacity when disabled

src/components/combo_box/combo_box_input/combo_box_input.tsx

@@ -269,7 +269,7 @@ export class EuiComboBoxInput<T> extends Component<
     }
 
     let icon: EuiFormControlLayoutIconsProps['icon'];
-    if (!noIcon) {
+    if (!noIcon && !isDisabled) {
       icon = {
         'aria-label': isListOpen
           ? 'Close list of options'

src/global_styling/reset/global_styles.tsx

@@ -73,6 +73,11 @@ export const EuiGlobalStyles = ({}: EuiGlobalStylesProps) => {
       ${fontReset}
     }
 
+    // Chrome has opinionated select:disabled opacity styles that need to be overridden
+    select:disabled {
+      opacity: 1;
+    }
+
     button {
       font-family: ${font.family};
     }

upcoming_changelogs/6768.md

@@ -0,0 +1,8 @@
+**Bug fixes**
+
+- Improved the uniformity of dropdown components by hiding the dropdown icon of disabled `EuiComboBox`s.
+
+**Breaking changes**
+
+- EUI now globally resets a default Chromium browser style that was decreasing the opacity of disabled `select` items.
+