Sources and Uncertainty
The principal sources record little more than Macarius's name, rank, and feast. The OCA synaxarion lists him on October 6 as "Monastic Martyr Macarius of Saint Anne Skete, Mount Athos" with the note that no information is available. OrthodoxWiki's October 6 calendar names him as "New-Martyr Macarius the monk of St. Anne's Skete on Mount Athos."
The OrthodoxWiki entry for the day also carries the notation "at Kion in Bithynia" — possibly indicating a place of martyrdom (Kion, or Cius, an ancient city on the Sea of Marmara in Bithynia, near modern Gemlik, Turkey) — but the page does not explicitly attribute this location to Macarius rather than to another commemoration on the same date, so it cannot be stated with confidence.