in Geany, press "tools" > Configuration Files > geany.css Ctrl + F ": image(-gtk-recolor(url("assets/scalable/small-checkbox-unchecked-symbolic.svg")), -gtk-recolor(url("assets/scalable/small-checkbox-unchecked-symbolic.symbolic.png")));" put #/ at the beginning. Put /# at the end. Ctrl + S Close, reopen. Checkboxes work now.
I mean, the screenshot does show the exact line, the exact commenting out characters and the exact location of the commenting out...... either way, at least you managed