Posting to a closed issue, as I don't want to open yet another issue for this.
My setup: geany 1.36 (built on Mar 22 2020 with GTK 3.24.14, GLib 2.64.1) on Ubuntu 20.04.2
I can confirm the problem, not only with Default Monospace font (set to DejaVuSansMono.ttf), but also with quite a few other fixed-type fonts on my system.
Considering the number of people being affected by this (myself included), would you guys consider changing the default `line_height=0;2;` so there is no need for users to fiddle with config files ?