“No still photographs were destroyed, that’s just silly. I hope you’re not one of those Moon hoaxer nutjobs.”
No. Sorry. It is well documented that NASA cleaned out a huge amount of stills and videos. You’ll just have to go looking for the documentation yourself - I long ago lost or forgot the links to the various places. Much of it took place in the early 80s and 90s, and I’ve been through several computers and many hard drives over the years and some data was lost or destroyed in the transitions.
NASA is very infamous for ‘disappearing’ many things (including lunar rock samples) over the years during the various changes in management. This has nothing to do with hoaxes - its often put down to various things, but usually just plain government bureaucracy at work. Things that should have been kept have turned up in private collections or at auctions. Many of the remaining stills are copes of copies of copies and so on for generations - much of the clarity of the lost/destroyed original is no longer on the images; they are very badly degraded - especially those available as highly compressed .jpegs.
Just recently someone found the original images of Armstrong as he set food on the moon and has been restored somewhat. Remember the formats in use then for video images are nothing like today’s and conversion often does not go well - you actually have to see the original played on the intended tech, not your PC or digital TV.
During recent times, all of the US Navy’s Clementine hi-res images of the moon remain classified. Many of the Mars and other lunar missions images and data are no longer publicly available. Perhaps that material still exists at the various NASA sites and JPL. To access it, you’d have to put in a request (but you need to know the catalogue numbers and so on - which again are not publicly available), or else visit and look through their respective catalogues personally - a task which could take days or weeks.
I think I read somewhere that there exist a project to digitize the remaining material from Apollo, but it will take many years to complete - if it does not run out of money and interest before it is finished.
I believe that's what you're remembering. I'm unaware of any other large-scale loss of worthwhile Apollo artifacts.
Clementine was a joint effort by NASA and the DOD, specifically the SDI program. I'm not able to find corroboration that there are large numbers of Clementine images that remain classified, but if there are, it's because the government wants to keep their imaging capabilities a secret.