Hi Rick_2023,
You started from a great resource: How to download macOS - Apple Support
Be sure to check out the section "If you need help" from the same article, and also found below.
"If you need help
If you're having difficulty getting the links to work, try again using Safari. It's in your Applications folder.
If you need more storage space to download or install, learn how to free up storage space.
If the macOS that you want isn't compatible with your Mac or the currently installed macOS, the installer will let you know, and the App Store might prevent you from downloading it. For example, it might dim the Get button, say that the macOS is not compatible with this device, or say that the requested version of macOS is not available."
Should the issue continue test installing while in safe mode. You can find additional details here: If an error occurred while updating or installing macOS
Cheers.