Reinstall "Import Configuration" Drive Format

[smajor]

I've had OpnSense for years, but might move to new hardware.  Over those years I've tried and failed many, many, times to get my configuration imported at install time.

Daily, I don't live in the *nix world. My desktops are Windows or Mac.

What format of, say, a USB flash drive is OpnSense expecting to find that contains my config? Is there a formatter for Mac/Windows that I can use as well as a tool to copy the config onto it?

Thanks for any advice!