The desktop operating system is the platform on which everything else runs: the kernel, drivers, file system, updates, security features and the environment in which employees work. Organisations choose it together with device management, application compatibility and support arrangements. Windows and macOS are the usual reference points, with Linux distributions as the main alternative.
Control over the operating system determines what you can verify and change. Proprietary systems decide how updates are delivered and which cloud accounts are encouraged or required during setup. Hardware support, drivers and line-of-business software constrain the choice, and device management usually depends on a vendor cloud. With open-source systems, the code and package sources can be inspected and mirrored, but support and long-term maintenance depend on the distributor and the community. Because every endpoint runs an operating system, patch cadence and supply chain security also fall under the risk management that NIS2 expects.
When evaluating a European option, look at the length and predictability of security update support, availability of enterprise management tools, compatibility with your key applications, hardware certification and commercial support under contract. A pilot with a small user group, run before any wide rollout, shows which applications and peripherals cause problems.