On Linux, after copying a rectangular selection into the clipboard, it is possible to paste it into existing text while maintaining the rectangular structure (and not insert newlines where none existed before). On a Mac, this appears to be broken.
Geany 1.37 Using GTK+ v3.24.20 and GLib v2.66.0 runtime libraries
System Version: macOS 10.15.7 (19H15) Kernel Version: Darwin 19.6.0
Example. I want to move the two lines of "hub." into the links above: 
But when I do a rectangular select (using the mouse since the keys don't work.......that's a different issue), the result of pasting does not at all look like it would on Linux. It looks like this: 
When it should look like this: 