Docker has always used microVMs (well since 2016)

Docker has used microVMs since 2016, building a custom "library VMM" called hyperkit (now Docker VMM) embedded within the Docker application to provide better security and performance than traditional virtual machines like VirtualBox. This minimalist approach, based on LinuxKit, enabled features like rootless operation and careful control of the host/VM interface, and now forms the foundation for both Docker Desktop and Docker Sandboxes. The technology demonstrates that Docker was ahead of the curve on microVM adoption, contrary to the recent industry buzz around the concept.