The combobox coding example in ARIA 1.2 does not include an accessible name for the listbox, according to the spec, listbox requires an accessible name.
https://www.w3.org/TR/wai-aria-1.2/#combobox

The APG call on 4/19/2022 discussed whether a listbox that is controlled by combobox needs an accessible name and is associated with the following APG issue:
w3c/aria-practices#2290