Hi, Henrik —
Thanks for the question.
St. Anthony the Abbot was a Coptic
Christian, but the Coptic Church
had not gone into schism during the
time he lived. It was in full communion
with and part of the Catholic Church.
He died in 356 A.D. The Coptic Church
went in Schism in 451 A.D. after
the Council of Chalcedon when they
rejected the current Christological
definition or dogma of the Hypostatic
Nevertheless, to this day, there
is a Coptic Rite in the Catholic
Church and those in the Coptic Rite,
would call themselves Coptic Christians,
as well as Catholics.
There are some that are in union
with Rome and some that are not,
but as far as Anthony is concerned,
he predates the schism, hence he
is revered by both faiths.