Steps to fix:
This also occurs for file pages with this detailed bug report: https://lists.sr.ht/~cadence/breezewiki-discuss/%3CAS8P193MB223835197E39BCF2F3088414C4699%40AS8P193MB2238.EURP193.PROD.OUTLOOK.COM%3E
Special:AllPages can include the File namespace, so supporting files requires no extra effort after categories are supported. It's the same change.