It's still pretty difficult to route a single-layer board with KiCad. Who still uses single-layer board these days? Pretty much everyone who does anything modern with a 2-layer PCB, the bottom layer is the EMC/RF ground plane, so there's only 1 effective layer. There really should be a "jumper manager" that allows you to add ad-hoc wires and THT/SMD resistors, perhaps with back-annotation. #electronics