Ideally, this should be mapped to alt+click as this is what vscode does and also we use alt+shift for the block caret.
Alright, I'm confused because I have command+control swapped on macOS - in fact it's ctrl+click for the block caret on Geany now. In this case I'd suggest that we use block caret (in addition to the current ctrl+click) also for alt+click so one doesn't have to remember which one is ctrl and which one is alt.