Implicit transaction costs show the cost of the bid-ask spread. These are external costs that depend on the difference between the middle price and the spread during order execution and do not arise from DEGIRO.
DEGIRO is required to display the implicit transaction costs in the Annual Costs and Charges Statement. The implicit transaction costs are the difference between the price at which your order was executed and the middle price between the bid and ask prices at the time of execution.
These are not separate costs that have been charged but are included in the purchase price of your shares. DEGIRO has no influence on these costs.