Is using screens and multiply computationally expensive?

Whether it's computationally intensive in Illustrator is not really your concern. You're not running the game in Illustrator. Your concern is whether the exported result is data intensive in the actual game environment, which will in all probability have been flattened to simpler constructs than the live effects in Illustrator.

So answering the question would require more information about what you are actually delivering.

JET

Hi, obviously more details are included in the realization of the graphics (lights, shadows, etc.) the greater the work that the computer will have to manage to guarantee an excellent experience and fidelity of the image created.

I don't know much about SVGs and game art, but I do know illustrator. Multiply and Screen effects will be "expensive" if they go across rasters or gradients. But going across flat art will not take up too much processing speed.

So you export SVGs and those will be in the game?