There is different types of software.
Embedded software is flashed straight to "embedded systems", i.e. special purpose computers such as ESP32-boards.
Operating and file systems are used to run computers that provide the basis for home automation.
OS application run on operating system level and are typically "infra"-type of applications, i.e. they provide technical capabilities for actual home automation applications.
Container applications run in Docker and Kubernetes containers. Home automation capabilities are are offered by these systems and most of applications are accessible by end user.