This might be completely off-base, but have you tried different baud rates? The error looks like the wrong port, but the last part of the error message, "Check if the device is connected to this port" makes me think it has the right port, but can't initialize the focuser.
Also, you might try scan ports, and usbserial-0000000.
Thanks,
Dave
Dave Allmon
12" LX600
SBIG STF-8300EN
Raspberry Pi 4 Indi server
Linux client