What USB to Serial cable are you using? Prolific, FTDI etc?
If it detects the COM port exists it should be able to open it, even if no description is shown.
You could try manually changing the COM port from COM6 to something else.. 1,2,5 etc.. and see if that changes anything.
Do this from Device Manager, right click the com port, select properties > port settings tab > advanced then change the port number from the dropdown.
Screenshot 2025-01-31 232802.png
Unfortunately I cannot debug and reproduce the error in the source code as I don't have a PC to run Visual Studio without lagging, crashing. My main PC died at the end of last year so until I have some spare funds to replace it, I can't to any debugging or implement any bug fixes or updates.

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