Use iWork'08 disk on MacPro Catalina 10.15.7?

You can't. It's 32-bit software and won't run on Catalina or newer.

(261563)

Grant Bennet-Alder wrote:

They should have been pre-installed on a new Mac.

I'm not sure if they were preinstalled – or if they were free, but needed to be downloaded from the App Store.

That could make a difference if someone never downloaded the applications while the versions in the App Store were still compatible with a version of macOS that their Mac could run. I believe that the current versions of the applications require macOS 14 (Sonoma) or better – unless Apple has raised requirements again. Which means that if they're in your "Purchased" history one might be able to re-download older versions, but if one is just now getting around to downloading them for the first time, one might be out of lock.

the main iWork applications, Pages, Numbers, and Keynote are available in versions that do run on your current Mac. They should have been pre-installed on a new Mac.