As some other comments on this post have mentioned, there is a a treaty known as the "Lugano Convention", whose parties are the EU (as a whole), Denmark [0], Iceland, Norway and Switzerland; post-Brexit, the UK wanted to join in its own right, but the EU refused. Under the Lugano Convention, if you get a judgement in a French court, you can then apply under the convention to have a Swiss court enforce it; however, there are exceptions which the Swiss court could rely on to refuse to do so – but I have no idea what are the odds that a Swiss court would decide any of those exceptions apply.

[0] Denmark has an opt-out from this area of EU law, which is why it is the only EU member state which needs to be directly party to the treaty; it applies to the others indirectly through the EU as a whole being a party to it

EU is a treaty, or lots of them.