Sosumi is a snap package based on macOS-Simple-KVM that makes it easy to download and install macOS in a virtual machine (is comes bundled with qemu-virgil, which includes virtio-vga, a paravirtual 3D graphics driver). It does not ship with macOS, but downloads an installer image for macOS Catalina.
It's worth noting from the start that Apple doesn't allow installing macOS on non-Apple hardware, so to use this legally you must have Linux installed on Apple hardware.
After using Sosumi for a few hours on my Ubuntu 20.04 desktop, I can tell you that the installation takes quite a while (about 50 minutes on my system), and the macOS system may be a bit slow, but it's usable. So this may not be suitable to be used for heavy tasks, but it's perfect for testing.
This snap package, created by Alan Pope of Canonical / Ubuntu, makes it easy to install and run macOS in a virtual machine on Debian / Ubuntu, Fedora and other Linux distributions (after installing snapd), shipping with basically everything you need to get it running. You can find the snap package source on GitHub. If you don't want to use the snap package though, you have the alternative of using macOS-Simple-KVM, a set of tools to set up a quick macOS virtual machine in QEMU (accelerated by KVM).