@xiota I use Geany 1.37.1. I installed geany plugins already. In Lubuntu in ~/.config/geany/plugins/ there is only one file called "spellcheck". Even if I activate in the plugins the checkbox "Lua Script" and after restarting Geany there is only one file called "spellcheck".
The script basically just does what you described. Hides hbox_menubar, but during runtime without having to edit any glade files.
And where should be this script?
Thank you for an answer in advance.