These were the 'hieratic' and 'demotic' scripts, which can crudely be thought of as merely different fonts of the hieroglyphic alphabet. The rise of Christianity was responsible for the extinction of Egyptian scripts... Then, towards the end of the fourth century AD, within a generation, the Egyptian scripts vanished.

Why did hieroglyphics die out?

Monumental use of hieroglyphs ceased after the closing of all non-Christian temples in 391 by the Roman Emperor Theodosius I; the last known inscription is from Philae, known as the Graffito of Esmet-Akhom, from 394.

What happened to hieroglyphics?

Eventually, Egyptian hieroglyphs were replaced by the Coptic script. Only a few signs from the demotic script survived in the Coptic alphabet. The written language of the old gods plunged into oblivion for nearly two millennia, until Champollion's great discovery.