As a Cisco Employee, I would have thought that you could have found the answer via your internal channels rather than posting in a public, community supported forum.
I think you do not understand what the HDMI output on the Desk Pro is there for. It's for mirroring what is on the main call display, or as a separate screen for content shared within a call. It is Not for connecting an additional monitor (other than the Desk Pro itself) to an attached PC.
If you check out the Connecting a second screen to your Desk Pro (webex.com) documentation, it states the modes that the HDMI will operate in, and what will display with each setting.
If you want the best of both worlds, you could connect the monitor to both the PC and the Desk Pro (on different inputs) and then switch between those inputs for either your content or PC viewing needs.
Wayne
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