Travelers must have a visa or prior approval document
Trekkers and mountaineers must have a confirmed hotel reservation that allows at least 7 days shielding or quarantine in Nepal.
Trekkers and mountaineers must possess a medical travel insurance with international coverage of at least USD 5,000 that covers COVID-19 before traveling.
Children under the age of 2 are exempt from presenting a COVID-19 test.
Travelers with proof of recovery from the virus within the last 90 days prior to boarding. Proof of a recent positive viral test and a letter from your healthcare provider or a public health official stating that you were cleared to travel.
More info at the CDC site
Travelers who did not get tested, are advised to stay home and self-quarantine for 10 days after travel.