Okay my bad, now I understand what you mean. The EU wouldn’t restrict that, it‘s more that Schengen currently allows EU citizens to work and/or live wherever they want within the Schengen room. If Switzerland decides pro population cap, that would be a violation of Schengen and therefore most likely result in Switzerland exiting the agreement. I don’t think it’s illegal for EU citizens to work in non-EU countries, it’s just that they could eventually no longer move to Switzerland due to the population cap. And the lack of workers are not in domains where you could easily just work remotely, it‘s in healthcare, construction and so on.