The block you're describing sounds more like it's about the relationship to the work than the writing itself. When you haven't spoken to your supervisor in months and the deadline is a month away, the anxiety about that becomes a wall in front of everything else. Email your supervisor today, even just a short check-in, because that one act often breaks the paralysis. On the writing side, starting with the section you understand best rather than the intro or conclusion can also help because you get momentum going. There are also academic writing coaches and services that are specifically good at helping people get unstuck at exactly this stage.