Equity/RSUs in pre-IPO company


I have read in other answers that if we receive RSUs in a company and the stock is not halal for investing, we have to donate at least the capital gains.

How would one determine this for a pre-IPO company? First of all, how can we even figure out whether the stock is halal or not, and secondly, how would we evaluate its capital gains over the years before IPO? Do we just go based on the last valuation of the company and what it was estimated to be worth whenever there is a valuation?