They don't get electromagnetic interference, but they do suffer from attenuation and pulse broadening. Toslink is designed to be cheap, robust and easy to connect, so it is limited to a maximum length of 10 metres for polymer fibres.
Last lockdown I managed to channel a minor breakdown through unwise hifi experimentation. You might have noticed. I’ll try not to do that again, it seems that since I stopped fretting and just started enjoying listening to it my system just gets better and better.
Can’t fibre optic runs be as long as you like without picking up external interference, with it being light and that?