I'm not terribly familiar with Geany, so don't take this as a confirmation that it's not possible, but Kate, which is sort of KDE's Geany, does have vim keybind

I'm not terribly familiar with Geany, so don't take this as a confirmation that it's not possible, but Kate, which is sort of KDE's Geany, does have vim keybindings. With Geany being a lightweight IDE, I'd say Kate is a feature-rich text editor, so it's not quite the same, but maybe it works for you nonetheless.