During simulation, Flight.jl uses multithreading to concurrently handle the simulation loop, the built-in GUI and any attached I/O devices. Therefore, if you intend to use its interactive or I/O capabilities, you will need to start Julia with multiple threads enabled. You can find out how to do this in the manual. However, if you are using the Julia extension for VS Code, the easiest way is to add the following entry to your settings.json:

"julia.additionalArgs": [
    "--threads=auto",
],

This should work well for most CPUs and use cases. If you run into issues, you can set the number of threads manually to cover your specific needs.