FastPass is reporting that a requires an ARIA child role of textbox; however, based on this GitHub combobox pattern accessibility thread, the issue is that the rules is adhering to the ARIA 1.1 spec and not the latest ARIA 1.2 spec which does not require it.
I believe FastPass utilizes axe-core as its accessibility rule engine and I based on request 2505, it does not appear they have completed the work to adhere to this combobox spec in this specific situation.
Is the best guidance to wait for axe-core to complete the work or can the rule be disabled for now?
The automated checks in Accessibility Insights are powered by axe-core and we try to maintain our rule set close to the axe-core rules. In general, ARIA 1.2 is not an official recommendation yet but in particular for this pattern, from the linked GitHub issue in the Axe-core repo, the last comment is that this will be taken up in the 4.3 release. This rule impacts more than just comboboxes (the rule checks several ARIA roles that are parent roles and require children attributes) and turning it off would mean not catching issues in many widgets.