It's only illegal if the law is enforced and the US federal government gave up on anti-trust enforcement a long time ago and any attempts to re-awaken it get nerfed quick.
e.g. "Execs can no longer vacation in or transit through France without threat of arrest because they've ignored a legal directive."
See e.g. Oliver Schmidt of VW who was arrested on vacation in Florida from Germany, and served seven years in prison. Or Meng Wanzhou of Huawei.