The qhy_ccd driver is indeed the correct one. The polemaster is effectively the same as the QHY5L-IIM.
There is support now in the indi_qhy_ccd driver as a firmware blob has been added to the SDK. There are some issues with using the Polemaster as a capture device, which I suspect was intentional. Using it as a guider with short exposure times will work. Using longer exposures, 10s and up, introduces some issues with the camera.
I am seriously considering getting a QHY Polemaster, but I do not want to have to boot to windows to do the polar alignment process if I can avoid it. Are you able to polar align with the Polemaster under Ekos? If so, how are you doing it? Secondly, I think it's outstanding that it can also work as a guide camera. That makes it even more appealing. I do have a question regarding guiding with it though. I have several different OTA's. Some are wide field (120mm refractor) and some are pretty long focal length (8" RC). Do you think the Polemaster would be able to effectively guide both of these OTA's on the same mount? What is the aperture and focal length of the Polemaster? Have you used it for plate solving as well?