Check if the user machine's GPU preference is supported in PRE. For more infromation, see Recommended graphics cards.
Intel supported graphic cards recommended and supported by PRE might be displayed as unsupported.
Once you make sure that the card is supported and the driver version is compatible, request the user to share screenshot of GPU-Z and check if OpenCL is supported.
If OpenCL is unsupported, ask the user to update the driver version of the GPU and see if this solves the issue.
If the user's machine already has an updated driver version, use 'hit and trial' on old driver veriosns till you find a version that supports OpenCL.
Connect with the product team to know the possible/required driver versions.