One of the easiest way to install HA OS is to use the ready-made Virtualbox image. The only minus here is, that it is not possible to monitor HA OS resource usage. Thus I can’t see, whether it would be reasonable e.g. to assign more RAM for the instance.
Feature Request: please allow installing Virtualbox addon into Home Assistant OS, on the Virtualbox image.
Thanks @nikito7. This solves most of problems, i.e. now I can monitor the state. However, I would still like to have the full addon capability, as it provides more flexibility in interacting with the system running in virtualized machine. This is why I don’t mark this as solution, sorry.