Very few UK ATOs gained EASA approval before exit day, I'm afraid. At the moment the licence conversion UK to EASA involves pretty much the whole licensing process except the hours. ie pass all the ATPL theory, pass CPL/IR. You may be exempt approved training - this depends on the licence you hold and the one you are going for, and the attitude of the issuing state and supervising ATO - but I think you will still be expected to do 'training as required' before the flight tests. The easiest transition is if you have passed ATPL theory, held an EASA IR before exit day, and can find a compliant Authority in which case you may/should get credit for ATPL theory, get an EASA medical and take an EASA ATPL skills test. You have to have the hours for an ATPL to do this, if not it's a CPL by a longer route. The date of Dec 2022 only affects CAA recognition.