Edge driver to Associate Eaton Dimmer Switch RF9642 does not show up for my device

The IDE is being discontinued and the information in it (for the most part) is unreliable. You should check the API Browser+ which pulls data directly from the ST APIs and provides a lot of the same information that used to be in the IDE.

Also, from what you describe, the master dimmer is using an Edge driver, so you are able to switch to other compatible Edge drivers. The accessory dimmer sounds like it is still running a DTH and you can’t change from a DTH to an Edge driver. The device needs to be excluded and re-added so that it picks up an Edge driver. If you have a custom DTH installed for that device, you need to delete the custom DTH after you’ve excluded it from your hub.