UART-to-USB serial connection

I am trying to get the “USB to UART serial console cable” working on an M2 mac:

The drivers appeared to install correctly, and i’m pretty sure i’ve attached the cables to the right pins (and not the power cable - Raspberry Pi 3 is being powered by USB.

I’ve also added the necessary line to the boot config.txt.

All i see with ‘screen’ is a flashing cursor top left.

I’ve used this technique in the past (Model A Raspberry Pi i think!), so i have seen it working, but haven’t tried recently!


What version of Pi OS is the Pi 4 running? I ask because Bookworm uses a different location for config.txt.
It’s now in /boot/firmware/