Steps to reproduce:
Accessibility score of 100
Accessibility score of 91 (lighthouse which is included in google chrome)

The axe plugin is telling me as follows:
Fix the following:
Required ARIA child role not present: textbox.
For each of the mat-selects on the page.
I'm seeing same results on my app, which is running with @angular/material 10.2.7 and latest of angular 10.x.x.
Currently the role of the mat-select is combobox, which according to documentation of a11y indeed requires a child role of textbox: https://www.digitala11y.com/combobox-role/
The warning occurs because of the following unmet requirement
https://www.w3.org/TR/wai-aria-1.1/#combobox
Authors MUST ensure an element with role combobox contains or owns a text input element with role textbox or searchbox and that the text input has aria-multiline set to false.
Adding an input element with role="textbox" in the select template fixes the issue.
Note: for ARIA 1.2, the textbox is not required anymore:
https://www.w3.org/TR/wai-aria-1.2/#combobox
This is working as expected and accessibility checking tools haven't been updated to account for the new pattern. See the discussion after https://github.com/angular/components/pull/20082#issuecomment-686622547.
thanks! :)
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Most helpful comment
This is working as expected and accessibility checking tools haven't been updated to account for the new pattern. See the discussion after https://github.com/angular/components/pull/20082#issuecomment-686622547.