At Moses' time (maybe around 1600 BC), there were actually not even any organized written languages yet. Only symbol systems such as Egyptian hieroglyphics existed, and they were not really languages at all.
Another date widely accepted for Moses and the Exodus is the 1400's BC. Egypt, Sumer, Greece are examples of cultures with types of writing which were in existence by then.
For a long time, scholars believed there was NO writing whether symbolic or otherwise in Moses' day. This has been shown to be be false.
According to whom?
Moses wrote as God instructed him to.
And I don’t think he used invisible ink.
I suspect he could read the Hebrew of today except for the new vocabulary from modern life.
The syllabaries and alphabets are derivative from the hieroglyphs and ideographs.
The original writing system, Sumerian, is actually a highly styalized hieroglyphic system.