My MacBook Pro OS says it can’t support the numbers program I have

If you never owned/downloaded Numbers in the past, I don't think you can get an older version compatible with your operating system. If you have downloaded Numbers in the past under the same user ID you are using now, you should be able to find it in your purchased items in the App store. Click on your name in the bottom left corner in the App Store to see your purchased items. If it is on the list, it should let you download a compatible version.

I don't know why Apple won't serve up older versions for all of the people with older operating computers. I suppose they want everyone to either buy a new computer or use their iCloud version.

Do you have Numbers available in your Previous Purchases in the Mac App Store?

If not, then LibreOffice will probably work.