IoT devices are starting to use hardcoded DNS servers instead of using the one provided by DHCP, which negates the benefits of Pi-Hole on those devices.

For now, I've configured my router to force all UDP port 53 traffic to my Pi-Hole which overrides what I mentioned above.

But, in the future we may start to see IoT Devices hard-code DoH servers which will be harder to force over to the Pi-Hole.