Orthodox Christian here. The “Old Calendar” (Julian) is still in use in the Eastern Orthodox Christian Church (some). The Russian Orthodox Church (that Putin has in the front) are under the Old Calendar. Many EO Chruches have adopted the New Calendar that is common to the remainder of the word. Outside of some of the EO Church’s Liturgical Calendars the New Calendar (Gregorian) is the common calendar for the entire world. Everyone uses the Gregorian. All of these posts that reference the Old Calendar in regards to “Worldy” (outside of the Orthodox Church) seem to be date guessing, or re-arranging dates if something doesn’t happen at a certain time. As an example if a date goes by and nothing happens, then a post will appear referencing that it can still happen 13 days later. When the 13 days go by and nothing happens it ends up being another wrong guess at a date. Jesus said himself (and I paraphrase) that we will never know the date and time.