All OSes are a collection of lots of different software that work together to run your system.

For Linux distros, that includes kernel packages (the core of the OS), but also a huge range of software to make the desktop work, apps you run (office software etc) and more. They are all separate projects, constantly working on and releasing updates at their own paces. There are new software releases all the time for all sorts of things.

If you install a Linux point release Distro, like Ubuntu 22.04, you get the OS and a snapshot of lots of different software they have chosen to package. Then after install you will receive constant minor patches and security updates, but the main software doesn’t get major updates. For example, if Ubuntu uses say version 1.0 of your desktop (e.g. Gnome), and the Gnome project then releases 2.0, you won’t receive that. You’ll just receive patches and security fixes for KDE 1.0, but not big updates for new features or changes. This allows Ubuntu to keep 22.04 stable and working predictably for people, and means they don’t have to retest the whole OS to make sure it works and stays secure. All they have to do is test the security patches, make sure those work well with the existing OS and then release that to users.

But overtime Ubuntu 22.04 inevitably falls further behind all the major releases of the software they use, and people are missing out on more and more new features, more major bug fixes and more. The desktop environment for example might have released version 2.0 with new features, and the Office software may have released 2.0 with new features, and 100s of other components the same even in just 6 months. So the distro maintainers then build a whole new version of the OS with all the big changes they want to include, and release that as 22.10 in October 2022 - this is their next 6 monthly point release. People can chose to stay on 22.04 and just get security patches (so the OS is stable and safe) or decide to move their PC to 22.10 and get the newer software.

This is a constant process. Ubuntu is on a 6 monthly release cycle, and people can chose when they want to switch; they can do it every 6 months or less frequently if they want. Ubuntu and other distros also have LTS releases - Long Term Service releases - if you use that version, it is maintained for a few years as is, except for patches and security updates. Not everyone wants the latest version of software, they may just want something that they know works and they get on with using it.

Another model is rolling releases where the Linux distro constantly rolls out new updates for all the components. This can even be weekly, or near enough daily; for example OpenSuSE Tumbleweed is a rolling release. People might not update every day but the maintainers are constantly rolling out the latest versions of software (after some testing to make sure it works) so that end users can keep bang up to date on near enough everything. This is riskier than a point-release, and sometimes bugs get through that have to be undone, but it allows those who want cutting edge systems to have them. OpenSuSE also have a point release version Leap which updates once a year, and is also developing Slowroll which works on a monthly release cycle.

Windows actually does something very similar to the “Point Release” system for new features and major changes, although the updates are all closed source and under Microsofts control. Windows 11 has had major annual updates 21H2, 22H2, 23H2, 24H2, and now 25H2. One big difference though is that Windows updates are only Windows and Microsoft provided software; all the rest of the OS including drivers the user has to update (or sometimes Windows Update manages). On Linux, much more of the system is usually updated by the Distro, and the user generally updates a much smaller proportion themselves (e.g. maybe their Nvidia drivers, and their flatpaks).

The big point releases are not about increased security, they are instead more about getting feature releases out to users from lots of different projects. The security side is managed by constant patches and smaller bugfixes rolled out within each major version.

If you’re on a 6 monthly distro, you probably won’t notice big changes, you’ll more likely see lots of smaller changes. The really big changes (like KDE moving from 5.0 to 6.0) are less frequent - maybe every couple of years - while the smaller but still substantial changes are frequent - like 6.2 to 6.3. You will notice when you move from 5.0 to 6.0 but when you move from 6.2 to 6.3 you’ll have lots of smaller nice changes but not a major change to your desktop. So while it seems like little is changing, lots of small things are changing all the time.