Editora 0.18.3. Archived, so links from that release keep working. Read the 0.18.5 page →
View: Toggle 80-Column Ruler
view.toggleColumnRuler Show or hide the 80-column ruler.
How to run it
Open the command palette (M-x in the Emacs keymap) and search for View: Toggle 80-Column Ruler, then press Enter. It has no default keybinding, but you can bind one in Settings → Keymaps.