check this out - Webex Video Support
And Select video settings for Webex Meetings and Webex Webinars
Looks like 1080 is max for WebEx right now as you said:
Camera resolution—Change the maximum camera video resolution. You can select one of the following resolutions:
360p
720p
1080p
| Your account has to be enabled with the 1080p video resolution capability to see that option in the drop-down menu. On mobile, you can choose between 720p and 1080p video resolution |
Thanks, Anthony
FedRAMP (cluster f)