US citizens who live in Panama and will be 18 by November 3, 2020 can vote in the Democratic Party Presidential Primary. Democrats Abroad, which is an official part of the US Democratic Party, has its Global Presidential Primary during the week of March 3 to 10. Global members will vote for their preferred Democratic Presidential Candidate. Events in Panama are March 3 in Boquete, March 6 in the Coronado area and March 8 in Panama City.
You need to be a member of Democrats Abroad to vote, but US citizens can join DA that day and vote.