They do not sell real shares in many cases – Webull: Investing & Trading Review

Most orders are internalized, payment for order flow, hedge fund buddies trade against you with Algorithms. If they do buy the real shares in their name not yours, they lend them out to short sellers to further work against your investment. You are better off with Fidelity or a direct register like Computershare if you want real shares in your name with real dividends and voting rights as a shareholder.
Review by BioDieselThis on Webull: Investing & Trading.