There's very little I 'Know' -
(on this or any other subject)
I trust that you glimpsed the PBS presentation on the topic (?)
I've not further delved into verifications of the claimed source material. Yet.
I note though, that he was not given to soul-baring self-analyses for the amusement and edification of contemporaries or posterity.
As to
he accepted the goals of alchemy wholeheartedly. Like all alchemists, he thought that lead to gold was a step along the way to completing the Great Work: which was to create a Philosopher's Stone.
The last belief I'd advance, from 2006 - is that I 'understand': the deepest mindset of a one such as this Man. No, you cannot say, "wholeheartedly" any more than I can pretend assurance of his level of awareness of the esoteric aims (of at least some..) of the 'alchemists'.
By that I mean: that the lead/gold plot was for these ones, merely a cover for their delvings; a necessary ploy for keeping at bay, the (variants of) Church Censors and er, incense censers / the pecksniff Ashcrofts and Foulwells du jour.
Still, since any regard at all of the 'Philosophers Stone' is an inherently metaphysical quest - I do not think it presumptuous to imagine that such an intellectual Giant as Newton would have been quite aware of the metaphors he was immersed in: and to suppose that he was seeking not merely.. some mathematical thesis next to 'prove' - on the scale of the physics of the phenomenal world. But that will forever-be: a Guess.
(We shall not ever explicate the mind of Newton, much as anyone would wish to - he be daid.)