Apple explains the difference between updates (these are updates within a version number, e.g. from 12.1 to 12.2) and upgrades (i.e. from iOS 15 to iOS 16). Apple also explains who can make these updates if the device is managed, for example in a school or company.
An important fact for all Mac users is hidden as a small note on the page: the fact that older operating system versions are no longer officially maintained and are therefore considered safe. So far, one could assume that Apple always fully supports three versions: the current one (Ventura as of now) and the two predecessors (currently Monterey and Big Sur). However, Apple writes in the support document:
Note: Because of dependency on architecture and system changes to any current version of macOS (for example, macOS 13), not all known security issues are addressed in previous versions (for example, macOS 12).
So Apple openly points out that the company no longer fully maintains older versions, even if security problems are known. This means that there are still updates, but these do not cover all known gaps. This can result in legal problems for users if the software used is no longer legally considered safe when using important data.
Since both the restriction for the use of the latest operating system version macOS Ventura from Apple on older hardware is artificially limited and the two older versions are only half-heartedly maintained, they are at this point on the OpenSource Legacy Patcher. This allows you to install the latest macOS version on older hardware.