No backdoors have been created. For reasons of "compliance" with UK Investigatory Powers Legislation, instead of acquiescing to a UK Authorities directive to provide access to all encrypted data, Apple have disabled the ability for UK users to enable the ADP feature.
Advanced Data Protection (ADP), an enhanced security feature introduced two years ago with release of iPadOS 16.2, was withdrawn for new activations at 3pm GMT 21st February 2025.
Removal of this enhanced level of security, previously used by only a minority of end-users, reportedly changes nothing for the majority of users that have not previously opted-in to this additional privacy measure - and returns the available to the default encryption baseline that existed prior to availability of ADP.
To be clear, for users in the UK that had not previously enabled ADP, nothing has changed other than losing the ability to enable this feature.
For UK users that have already enabled ADP, nothing will change immediately. All data benefiting from AFPs end-to-end encryption will continue to do so - however, at some [as yet undisclosed] future date, affected users will have to de-activate ADP.