If the company sells permissible products, and does not take riba-based loans, and does not deposit its money in riba-based accounts, then there is nothing wrong with buying their shares and benefiting from this incentive.

There is nothing wrong with giving money to the company to trade in currencies with it, on the basis that the company will have 20% and the remainder will go to the shareholders.

From examining the eToro website, it is clear that trading is done through the use of financial leveraging (margins), including interest-bearing overnight fees, and CFDs which are haram.