not sure why it couldn’t detect driver, but you can try to install the driver separately, it’s here:
http://raysfiles.com/drivers/ch341ser_mac.zip
during installation, you may need to go to Security and Privacy settings and allow the driver to complete installation, and may need to reboot the computer as well.
If the driver is successfully installed, when you plug in the device, open a command line window and type ls /dev/tty.wch* it should show a device like the following:
/dev/tty.wchusbserialxxxx
that means the driver is successfully installed.