You cannot remove the combo box options without extending/overriding the component. That said, yes, it is possible to hide the trigger, but the problem then is, once you disable the dropdown, I'm not sure how you could identify the elements you are typing.
You could instead keep the dropdown but show only matching entries to what was partially typed in the combo box? If interested in this, check the Form > ComboBox > Ajax Linked Combos example
, the second combo allows you to type the first characters of the chosen country's city to trim down the dropdown results.
This other example hides the trigger button, but also uses a custom picker to show the filter you entered, so it is a little more complicated: Form > ComboBox > Custom Search
Does some of these options help with the scenario you want to cover? You may consider looking up other combo box examples from the examples linked above; you may find something that really does it the way you need.