using idvd on a mac pro 2013 with big sur

You made 2 subtly different statements.

Are you trying to use iDVD the app or are you trying to play a DVD on your Mac? They are not the same.

iDVD is an application that Apple once provided for authoring home video discs.

As far as I know, they abandoned it without ever updating it to use 64-bit code. So Catalina and later can't run it. It's a shame, too, because iDVD made it very easy to create home video discs with nice-looking menus.

Macs still ship with a DVD Player application, even though it is now hidden away in an obscure system directory.

Short answer: you can't.

This is a slightly longer answer:

Hello, how can I use idvd on mac bigsur? - Apple Community