Since Windows 10 usually does not automatically recognize these older cables, the process involves manually forcing the correct drivers.
Before you give up, run through this checklist: how to install vag kkl 4091 on windows 10
This is usually caused by an incorrect driver version. Ensure you are using the specific driver for your cable's chipset (CH340 vs FTDI). If you'd like, I can help you: specific download links for the drivers. Troubleshoot a "Port does not exist" Explain how to read fault codes once you're connected. are you trying to scan? Since Windows 10 usually does not automatically recognize
Step 5: Configure Diagnostic Software
Important: Also ensure the port settings match these values (from the same Port Settings tab): how to install vag kkl 4091 on windows 10