Numbers can’t be installed on “Macintosh HD” because macOS version 11 or later is required.

If your operating system is older than macOS 11, then the message is correct because Numbers 12.0 requires that you have macOS Big Sur or later installed.

If you have never installed Numbers previously from the Mac App Store, then you cannot get the last compatible version for your version of macOS, and will need to use Numbers for iCloud, Numbers for iOS/iPadOS, or another spreadsheet application.

Launch the Mac App Store, and sign in with the same Apple ID used to install Numbers previously. If you are on macOS Mojave or Catalina, then click cmd+0 (zero) to bring up the Purchases panel. You should see Numbers with a blue cloud outline and down arrow icon. Click that, and you should receive a dialog offering to install the last compatible version of Numbers for for Mojave (10.1) or Catalina (11.1).

If you are on High Sierra or earlier, this is the older Mac App Store design, so sign-in with the same Apple ID, and this time, press the option-key plus the Purchased tab. If Numbers appears there with an update button, go for it, and it should get the appropriate Numbers version for your installed operating system.

True, unless you purchased it earlier.

But there's a free substitute,,,

Look into the Free LibreOffice, it handles MS Office files like Word & Excel, & Page Layout…

https://www.libreoffice.org/