Complex sentence: Although it appears that the Council of Chelsea approved of Lichfield's elevation to an archdiocese, Hygeberht, who was present, remained a bishop at its conclusion; he signed the council's report still as a bishop, not as an archbishop.
Split into simpler sentences: Although it appears that the Council of Chelsea approved of Lichfield's elevation to an archdiocese, Hygeberht, who was present at the Council, remained a bishop when the Council ended. He signed the Council's report still as a bishop, not as an archbishop.