For the record, under current US law, it is not illegal to have a sentence in your locally-stored notes on your phone outlining a plan to commit a crime. There has to be an overt act. The police in that instance could inform the intended victim, surveil you, etc, but they would not be able to successfully charge you with attempted murder. It's not illegal to be considering committing a crime, even if you have a tendency to write down your thoughts.
The law in this particular case, which seems to be intended for threats that you actually send to someone, is being interpreted broadly to apply to any "threat" that you transmit to a server. So in your hypothetical, the legality would depend on whether your notes are backed up to icloud or not.
The law in this particular case, which seems to be intended for threats that you actually send to someone, is being interpreted broadly to apply to any "threat" that you transmit to a server. So in your hypothetical, the legality would depend on whether your notes are backed up to icloud or not.