Installation of macOS
New Macs come with macOS pre-installed.
To re-install macOS follow the instructions from https://support.apple.com/en-us/HT204904.
It is the users reposibility to ensure to always run a supported version of macOS.
As of July 2022 Macs that are enrolled in the Mac Self Service that run an outdated major version of macOS (currently anything lower than 10.15) will receive a monthly reminder that their macOS is unsupported.