I think it's more of a "if it walks like a duck and quacks like a duck." If you call yourself a journalist and have a record of reporting on things, then by this definition you are one. But you can't decide you are a persecuted journalist because you got arrested.
I've thought that there was nothing special about journalists such that you required a rigorous definition. Journalists shouldn't have more power than citizens, journalists are citizens that choose to exercise their civil rights to bring information to the public.
And this is the reason why BLM where vests that say press but then those same people are attacking police. They want to abuse the special privileges the press get.
The press doesn't get any special privileges. The law doesn't make a distinction between press and not press.
Certain organizations may get special privileges (press passes), but there's nothing legally binding about them. S citizen journalist is still a journalist under the law.
A journalist is someone that does journalism, just like a runner is someone that runs. The behavior "doing journalism" is simply reporting on something to an audience.
