The FTC is upset Amazon executives used Signal. Where do you begin with this?
If this was 50 years ago they would have just met in person, to avoid any kind of paper trail.
I don’t think “50 years ago it would have been easier to get away with it” is something judges and regulators generally go for.
But certain types of communication, especially by parties that have been told they are under investigation and are discussing the matter being investigated, must be preserved.