I close this now as the debugger plugin with GTK2 & 3 support was just released in Geany-Plugins 1.36.
Geany 1.36.Arch linux - no debugger found,no plugin to choice.No compiled file in directory.VIA Pacman Geany 1.36.Debian 10 Buster - no debugger found,no plugin to choice.No compiled file in directory. Builded from sources. Geany 1.36 Xubuntu 19.04 - no debugger found,no plugin to choice.No compiled file in directory. Builded from sources.
Issue not solved.