Question about VGA parameter in Transceiver Toolkit (Quartus Std 23.1)

In some contexts and device families, “VGA” (Variable Gain Amplifier) is used more generically to describe an analog gain stage, which can overlap with what is referred to as DC gain at the register level. Because the scripting API exposes a parameter named dcgain, and there is no visible VGA control in the API, it is a reasonable (but incorrect) inference that both refer to the same control.
 

However, as clearly shown in your Transceiver Toolkit screenshot:

• VGA and DC gain are separate parameters
• They can be set independently in the GUI
• They do not map to each other

I have checked the transceiver toolkit command documentation: https://docs.altera.com/r/docs/683552/18.1/intel-quartus-prime-standard-edition-user-guide-debug-tools/transceiver-toolkit-commands

There is no documented API for VGA, and it is not mapped to any exposed scripting parameter