I also have the same question. In my limited experience as the father of an eleven year old, it has continued to be much more productive to redirect profane or vulgar expressions of frustration away from people and towards problems ("Swear at problems, not people.") than to bubble-wrap their vocabulary.
Very genuinely, if your 11 years old need to redirect swearing to things and is unable to cut it in social situations, then he needs quite a lot of help with impulse control.
Because most of them, overwhelming majority actually, are easily able to not swear. They do swear when among peers only, but cutting it off when needed is really not an issue for them.
Everyone's different and harm/severity here is gonna be a wide range, but there's a lot of stuff I saw online as a kid that, as an adult, I really wish I hadn't.