He is not the president or vice president. This law would be more relevant https://en.m.wikipedia.org/wiki/Federal_Records_Act

Here, his signal comms are likely top secret and we would have no way of knowing if his office followed the legally allowed step of forwarding after the fact for many years.

There's similar record keeping for lots of officials. Government loves keeping records

And now we won't know, ever. Which is exactly the point of avoiding the system.