AFAIK it's the same in the USA, that's why one of the first questions when interviewing with a company is to ask them about their moonlighting policy if you do want to work on a side project.

That is not correct; assuming you are not using an employer’s equipment on employer’s time, and/or working on what the employer pays you to do for them or are working on something that is competing and a few other reasonable caveats.

It’s actually quite reasonable and logical.

https://french-business-law.com/french-legislation-art/artic...