Convert DMG to ISO for virtual image creation

I need to run a virtual image on a separate disk using Parallels Desktop. I have a Mojave image I pulled down but when I try the hdiutil util convert I get an error “hdiutil: convert failed - File too large”. If I try to just use Parallels it doesn't (of course) recognize the dmg as an OS image. There are multiple articles on this site about converting, but the ones I've seen are 7+ years old and based on experiences of the last 2 days, they'll just be useless because of changes to the OS. What's the best way to convert a 3.1gb dmg to an ISO so I can write it to a thumb drive for use?

Alternative: Is there a safe, Apple-supported/recommended site to download Mojave as an ISO?