It isn't an easy (or even enjoyable?) read but I found it incredibly thought-provoking. Like The Little Friend it is about someone seeking to mend things that have been very badly broken, trying to return to an earlier happiness, but again and again and unrelentingly finding it impossible to make that return. Culturally, that is a very central idea for us. The Christian story of fall and redemption, for example.
In The Goldfinch she takes it furhter than in The Little Friend, because she uses the metaphor of 'restoration' (ie furniture restoration) to interrogate different ways of bringing something back to its original, happy, condition.
As I remember (I read it years ago) the centrl character has a mentor who restores furniture in some sort of authentic, honest, way, but he himself is seduced into dishonesty in the way in which he approaches the same work. And alongside that dishonesty he is also paralysed in the way in which he approaches the idea of 'restoring' the painting to its proper place.
His failings and paralysis are attributable to the intensely traumatic way in which he was torn from his mother. It was too much to process, a fall that was beyond redemption -- except possibly for some smaller redemptions that I guess it is the role of the protagonist to discover and learn to tolerate as the best that is available.
Sorry, I know no-one wants to read this ramble, but I just wanted to work through my thoughts about the story: for some books, that is what is enjoyable about them -- the compulsion that they generate in the reader to try and understand