Pi-hole is blocking that domain by default in order to avoid clients from bypassing Pi-hole via Apple's iCloud Private Relay, see also Configuration - Pi-hole documentation.
Pi-hole does not initiate those DNS requests, it only answers them and makes them visible as your clients are sending them.
Why your devices would request resolution of that special domain if they presumably are not using Private Relay would be a question for the manufacturer or software developer of the device or software sending those requests.