Guatemala does not permit the entry of travellers who have been in the United Kingdom or South Africa in the 14 days prior to their arrival. This measure is not applicable to Guatemalan nationals, diplomats or foreign nationals who are legal residents in the country.
24 hours before your arrival, you are required to register via the Guatemalan Health Pass website. Once you have submitted your details, you must print the form and bring it with you.
Children under the of age 10, travelers with a medical discharge of a COVID-19 infection which occurred at most 3 months before arrival and have a medical certificate issued at least 10 days after being diagnosed, and travelers with a certificate of vaccination against COVID-19 if the last dose was administrated at least 2 weeks are exempt from presenting a COVID-19 PCR-RT test result.
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.