September 23, 2020 updates:

India (Persons of Indian Origin (PIO) card added)
Guatemala (updated but unclear what changed)
Hawaii (see below)

is: Starting September 1, all travelers flying to or transiting through Hawaii must complete a health form online. Paper forms will no longer be accepted, and United highly recommends completing the online application before boarding to avoid long wait times upon arrival and missed flight connections.

was: Starting September 1, U.S. travelers and those arriving from Guam must complete the form online at https://travel.hawaii.gov. Paper forms will no longer be accepted, and United highly recommends completing the form before boarding. International travelers will be provided a paper form in flight.

David