This relates to basic Geany capability, not a plugin.
To have symbols recognised they need to be recognised by the ctags parser, but I doubt it considers an include a symbol, its not a name in the program.
You would have to modify the ctags parser to do it, note its a separate project from Geany [here](https://github.com/universal-ctags/ctags).
Making an include symbol clickable to open the file would then be functionality added in Geany, but somebodys gotta code it.
You are aware that in the edit window you can select the include filename and <ctrl>+<shift>+o to open it as a workaround?