The front panel of a computer case is usually plastic. Isn't that unable to shield electromagnetic radiation?

If the chassis material is ok, before you use the CD-ROM slot, there is an iron block, the area is equivalent to the area of the CD-ROM panel, and each CD-ROM slot has it. So don't worry too much about the leakage of electromagnetic radiation. Of course, it does not rule out that some chassis manufacturers have saved that piece of iron in order to save costs. It's up to you to buy or not.