This is for geany 1.38 on MacOS.

On the Mac, the commonly used key combination for placing the cursor to the start and end of the line is

command+cursor_left : Start of line command+cursor_right : End of line

Command+cursor_right does not seem to have any effect in Geany. Checking the Keyboard assignments in the Geany Preferences, I can see that "Cursor start of the line" is assigned to "Home" and "Cursor end of the line" is assigned to "End".

The keys "Home" and "End" don't have a representation on the Mac keyboard. Of course I can re-assign those two functions to what I like, but I suggest that Geany for the Mac initially uses those key assignments which are commonly used on the Mac.