By default, advanced filters use autocomplete, i.e. when you start typing a value in the filter, the list of available values dynamically changes to display only strings with matching initial characters.
This autocomplete behavior can be disabled. To do so, go to Administration > Configuration > Advanced Configuration Options and set the "advancedFilterComboboxDisableAutosuggest" property value to "true".
Once it is disabled, you can still type the characters which will restrict the list of available values, but this list gets displayed only after you click the arrow icon in the filter field.