Personally I don't have an issue with the Air Force accepting the 747-8 jet as a gift.
However there needs to be conditions:
#1 Qatar must gift the aircraft with no strings attached. It becomes the property of the United States Government in perpetuity with no conditions. That at some point in the future, as determined by the US Government it can be scrapped to save on maintenance costs, donated as per direction of Congress, or sold to the highest bider. That since it was donated to the Air Force and not President Trump, that it would not be transferred to a private Presidential Libary organization.
#2 The aircraft will be used for at least 10 years by the Air Forces as an air show symbol at events around the world as a "Aircraft Good Will Platform" and will be open to the public to demonstrate the close friendship between the people of Qatar and the people of the United States.
#3 Due to security concerns and the costs of safety and national security deep inspections and the costs of retrofitting communication and anti missiles systems the aircraft will remain unmodified but will never fly with the President onboard or fly with the designation of "Air Force 1" nor will it be designated a VC-25(series) within the Air Forces inventory.
Under those conditions the US would be happy to accept.
WW