VirtualBox/Setting up a Virtual Machine/macOS Catalina

Compatibility
macOS Catalina 10.15.2 and 10.15.3 (and possibly every later version) are only compatible with VirtualBox version 6.1.4 or greater.

Installation script
The following installation script:
 * ...is free and open-source
 * ...requires only VirtualBox with its Extension Pack and dependencies that can be easily installed in a single command with most open-source package managers
 * ...downloads macOS Catalina, Mojave and High Sierra directly from Apple's servers
 * ...installs macOS without modifying the original Apple binaries and without third-party bootloaders
 * ...creates a VM that is compatible with OpenCore and can be exported (with manual modifications) to KVM/QEMU for near-native performance
 * ...runs on Linux, Windows (WSL, Cygwin), and macOS

https://github.com/myspaghetti/macos-guest-virtualbox - Push-button installer of macOS on VirtualBox