As you know, the ability to exchange one token for another on FlatQube is provided by the liquidity in pools. In the event that there is not enough liquidity in the corresponding pool, or the required pool does not exist at all, Cross-exchange will help you. The essence of Cross-exchange is to interact with several liquidity pools at once: Let's say you need to exchange token A for token B, but the corresponding pool does not exist. In this case, FlatQube will suggest performing a cross-exchange swap, in which token A will be exchanged for token C (interacting with the A/C pool), and then token C will be exchanged for token B (interacting with the C/B pool).
You should bear in mind that since you are interacting with two pools at once, your slippage tolerance, as well as Liquidity providers fee, doubles.