To answer your question about macOS, major version updates are yearly, things don't change much within the same major version, and you're never forced to update

To answer your question about macOS, major version updates are yearly, things don't change much within the same major version, and you're never forced to update by the OS. However, major versions only get 2 years of limited security updates after the next major version comes out, and major versions do tend to change things (i.e. the major redesign in Big Sur, or the new System Settings in Ventura). So probably not what you're looking for.