I just returned from 2 weeks in Turneffe. Stayed at Blackbird Cay Resort. The new villa rooms were the nicest I have ever stayed in. All rooms have screened in porches. The food is very good with an emphasis on native Belizean dishes. Blackbird is owned by a wealthy Belizean family and the staff seems to really like their jobs. The reefs are diverse and healthy. Underwater species diversity is good to very good. The divemasters spear lionfish which show up later at happy hour. The price was lower than Turneffe Island Resort. Now that I have stayed at both, I prefer Blackbird as it was smaller, fewer people, and fewer rigid rules to chafe. The single supplement was waived because I stayed longer than a week.
The Covid test in the airport - walk up, pay $75, get a nasal swab taken, wait 15 minutes and assuming you are negative, they hand you the report that the airline will require of you to board your plane.
The biting bugs of Belize - and they are everywhere except Half Moon Caye - are called doctor flies. They are like deer flies that bite people - slow enough to whack, though. Hydrocortizone and Benedryl creams are inneffective so avoidance is best.
Did you have air conditioning?