Quick summary of the technology is that there is two software parts for virtualization, the hypervisor and the virtual machine monitor.

First is the hypervisor that uses the hardware virtualization features of your cpu to emulate hardware interrupts and virtual memory paging. This part is usually buint into the operating system kernel and one will be prefered per operating system. Common ones are Hyper-V on Windows, Virtualization.Framework on Mac and KVM on Linux

With the kernel handling the low level virtualization you need a Virtual Machine Monitor to handle the higher level details. The VMM will manage what vm image mounted and how the packets in and out of the vm are routed. Some example of VMMs are QEMU, VirtualBox and libVirt.

Flint, the app being shown is a vibe coded web app wrapper around libVirt. On the bright side this app should be safe to use but it also does not do much beyond launching pre made virtual machines. As a developer the work you need to do is provide an Linux distribution (Ubuntu, etc), a container manager (Kubernetes, Docker) and launch your own containers or pre made ones from the internet (Dev Containers).