Cannot connect to Genmitsu L8 20watt with my mac

USB-C on the MAC?

If so and you are using a USB-C to USB-C to the laser, the MAC USB 3.0 might not downshift to USB 2.0 for the laser. The usual solution is to install a USB-A dirt cheap hub and a couple of USB-A to USB-C cables between them. This forces the MAC to downshift to USB 2.0 for the Laser.

Let us know if this works.