Coptic is the liturgical language of Coptic Egyptians, but their everyday language is Arabic.

It is. The Coptic Church is very much alive (although not widespread) and it uses the Coptic language.

Coptic

Coptic is the final stage of the ancient Egyptian language, which was used in Egypt from around the 3rd century AD until the 17th century. It is primarily known for being the liturgical language of the Coptic Orthodox Church of Alexandria and is still used today in religious rituals. Coptic is written using the Coptic alphabet, which is based on the Greek alphabet with additional signs for Egyptian sounds.

The purpose of the coptic language in antiquity was to allow individuals following the Coptic religion to communicate. In the present, the language is not spoken anymore though present day Copts us it in their church.