All humanitarian flights and those necessary to transport the medical supplies in the fight against COVID-19 are exempted from this measure.
As the months drag on and this pandemic persists, Panama's borders and airports remain closed. Continuing in consistent fashion, the government has announced another 30-day extension of the airport closure, restricting all international flights. As of now, the new projected date for reinitiating operations is set for Aug 20, 2020. Those operations may be able to restart, you'll need to check with each individual airline to see when they'll be relaunching their own routes.
This is the third extension of the border closure and airports, so we won't realistically know if this new August date is concrete or not. Only time will tell. Best to delay any travel plans until the reopening is confirmed.