Retail investors are famously locked out of the startup world. Robinhood is attempting to change that by allowing the general public to invest in a portfolio of what it calls “some of the most exciting private companies operating today.” To do this, the company that pioneered the commission-free brokerage model has secured access to eight startups — including Databricks, Stripe, Mercor, and Oura — grouping them into a vehicle called Robinhood Ventures Fund I. The fund, which also includes Ramp, Airwallex, Revolut, and Boom, set out last month with an ambitious $1 billion target, but demand for this novel way of investing in private companies was lower than expected. On Thursday, Robinhood announced the fund had reached a total fund size of $658.4 million — which could reach $705.7 million if underwriters exercise their full allotment. The shares, priced at $25 in the offering, began trading on Friday and closed the day at $21, a 16% decline.…