I'm on the latest docker tag ( Docker Tag 2021.10 Pi-hole [v5.6] FTL [v5.11] Web Interface [v5.8]) and I have also added BLOCK_ICLOUD_PR=false in /etc/pihole/pihole-FTL.conf.
Not sure what has changed, the iCloud Private Relay is not working any more and it used to work and I would have a different IP address.
Now I'm having both the BLOCK_ICLOUD_PR=false in /etc/pihole/pihole-FTL.conf and a new file in /etc/dnsmasq.d/xx-NXDOMAIN.conf with server=/mask.icloud.com/ server=/mask-h2.icloud.com/.
Earlier with just the BLOCK_ICLOUD_PR=false in /etc/pihole/pihole-FTL.conf did NOT work for me.
Yesterday there was an outage for iCloud Priavte Relay. There might have some changes involved which might have broken how pi-hole handles it. This is just a mere guess.
I'm not sure. It did not work for me unless I have created a file /etc/dnsmasq.d/xx-NXDOMAIN.conf with server=/mask.icloud.com/ server=/mask-h2.icloud.com/
and BLOCK_ICLOUD_PR=false in /etc/pihole/pihole-FTL.conf
Then after a restart of pi-hole and my phone I was able to get it working again.