It was wrapped up in all the Brexit information the CAA published at the end of last year. It must have been reasonably well known as I recall annoyed commercial drone operators moaning that they had to rewrite their Ops Manuals to change the references just after they'd rewriten them to refer to changes in applicable legislation.
The definitive ANO should be in Legislation.gov.uk and there is little point in the CAA publishing it separately and lots of possibility for it to get out of sync with the actual thing if they do so long term it's a sensible move. Unfortunately with all the legislation changes at that time the definitive source could no longer be guaranteed as definitive so for the time being the CAA appears to have come to an agreement with one of the companies that specialise in legal reference libraries to make their marked up version of the ANO available free of charge on the CAA website.