I have wondered this about a relative.
They can laugh but it’s not a joyful laugh - there is a sneer or contempt woven in - somehow!
They have no real passions of interests. Eg. music, art etc. (however, perhaps other types of narcissists eg cerebral may have certain interests or areas of expertise. I met what I believe to be a mid-range artist once who I was convinced was a narcissist and used his art (I believe) believe to get fuel and supply and status.
Back to my elderly relative - watches TV A LOT, occasional holidays, arranged by others, and superficial friendships and acquaintances. Very pragmatic view of life. A somatic narcissist, so interested in clothes and appearance and is well groomed, but nothing else, apart from maybe an interest in money. Now they are elderly, I really notice this more, because they don’t relate much to anything outside outside their day-to-day pragmatic self-interested existence.
So, I would say not much of an actual real personality. It’s really hard to explain.
I had a narcissistic friend who did seem to have some interests in life. Though I think they were pretty shallow and undeveloped. But when I went on holiday with her, apart from her petty jealousies etc, I noticed for the first time that there was a definite emptiness at her core. It felt like a really empty, depressing state. This is many many years before I’d even heard of the word narcissist.
So, I think there is either no personality below the facade, or a very weak and fragmented one