He lies, I think, most of the time because to him the ‘lie-reality’ where he did ‘good’ even though you give him evidence to the contrary and consequences feels better to him than facing reality. I lied (still do sometimes) because facing the truth would mean that I failed or trigger serious anxiety. Having your phone taken away hurts so much less than feeling like a hopeless failure once again! And I could blame my parents for that one If in my head it was a totally unfair consequence.
If your son is not a sociopath then he knows lying is wrong and probably does not want to lie so much, but the lying is giving him some kind of payoff (that might not make the most sense to you) that makes it the easier than just admitting the truth.
I don’t know what he specifically lies about, so I do not know exactly why he does what he does, but perhaps you will be able to find some common denominators. Perhaps asking him why a hypothetical person would lie about something like that and what the consequences are about lying about that will help you get some answers about what he is feeling.
About the not remembering what he’s done: Some things I do I do semi-automatic and have no memory of, such as where I put certain items etc., saying yes to a question/task when I’m focused on something else etc, but I would definitely remember making a mess of something or breaking something.
In short, finding out why, even though he most likely feels bad about lying, he feels so much worse admitting to the truth will help him a great deal, imo.