Is it permissible to buy shares in a company that sells permissible goods and offers to sell its shares to employees at a margin price (paying 20% and holding them for three years) with the aim of motivating them?

It is permissible to purchase shares in a company as long as it sells lawful goods, does not borrow from banks, and hardly obtains any usurious profits, while disposing of any usury that may mix with its profits (less than 1%). As for the condition of retaining the shares or not selling them for three years, it is valid and must be fulfilled, because its purpose is to serve the interest of the company (the seller) by incentivizing employees, not to restrict the buyer, and it does not contradict the requirements of the contract.