international travel – How to go from Terminal 4 to Terminal 1 at JFK during pandemic?

You can take the AirTrain, which seems to be running regularly, at least according to https://www.jfkairport.com/to-from-airport/air-train. The Airport Terminals Loop is the best choice, since it runs clockwise, and has then only one intermediate stop between terminals 4 and 1. Between the terminals, the AirTrain is free of charge.