When enabling HD video, there is more at play than just an SDK flag. For more information on this feature, please see the support article for group HD. Please note that there are some constraints mentioned in that article, so HD video will not always be available.
The following quote for the top of the page linked in my previous reply should be useful in answering your questions:
For the time being, standard video, not HD video, will be activated when 3 or more participants join a group meeting. HD video (720p) will be activated for 2 participants or when a Zoom Room or Conference Room Connector joins a group meeting. HD video (1080p) will only be activated for selective use cases such as large format broadcast events.
Additionally, please note that we do not currently support 1080p on the mobile clients or SDKs. 1080p is only available on the desktop.