"You must be logged in as root when installing this program."

It doesn't appear PrintMaster is supported with macOS 10.15+ as shown on the purchase page of the publisher's website (see the warning note in red):

https://www.broderbund.com/printmaster-v8-platinum-download-macintosh

Considering macOS 10.15 Catalina has been released for over a year and this warning still exists I don't think it will work and they have no intention of supporting macOS 10.15+. You can install an older version of macOS into a Virtual Machine (VM) so you can run this app if you want assuming you have an Intel Mac. I think it is time to move on to a company that wants to support the current version of macOS. It is always best to vote with your wallet as they say.

Since Best Buy gave you erroneous information, I would return it to them for a refund. Assuming that software that was introduced 10 years ago would still be compatible with the latest OS versions is somewhat "uninformed" shall we say. They should not sell anything unless they can guarantee that it will work.

I used to have that app a very long time ago; I do not believe they ever came out with an update after the 2011 release.

I agree with @babowa. If Best Buy gives you any problems giving you a refund make sure to show them the Broderbund website where it clearly shows it is not compatible with macOS 10.15 (and by extension macOS 11.2.x Big Sur).

Best Buy employees are not known for being very knowledgeable although I am sure there are a few here or there that are extremely smart and knowledgeable. Stores are always trying to push people to buy things whether it is needed or not and whether it will actually work or not. Almost all software today is distributed in digital format online either through the Apple App Store or the developer's or publisher's own website. It is best if you do your own research.

Good luck.

What program are you trying to install?

Does your user account have administrator privileges?