how do i install an older version of my macos?

Why-Not-Eco wrote:

how do i install an older version of my macos?

verify you are using the Safari browser to download/initiate the macOS links.

The older macOS installer backups on this server:

How to get old versions of macOS - Apple Support

Note that you cannot install an OS older than the OS your computer had when shipped new. Example: If it shipped with 10.14 Mojave, you cannot install 10.13 High Sierra.