Need help with Lightroom permissions settings after buying a new iMac

The destination folder is the folder you select as destination in the Import dialog. Your new iMac is no doubt running MacOS Catalina or higher, and in those MacOS versions you need to give Lightroom Classic special permissions to access certain folders:

Please provide details of how you got Lightroom Classic installed on your new Computer? Did you Download the Adobe Creative Cloud desktop application and use the App to install LrC or did you use the migrate feature from Apple?

As indicated by another responder you can set up permissions from the Apple preferences. It's possible to allow LrC full disk access or allow access to specific folders and files.

have the lastest Lightroom version as of 7/24/21. 

Yep, that is not exactly a good statement when looking for assistance, Would be better to state

I have Lightroom Classic version nn.n  (where nn.n is an actual number)

Perhaps you mean version 10.3?

My new mac is running Big Sur 11.5 

Start with:

https://nektony.com/duplicate-finder-free/folders-permission

that link probably better than:

https://support.apple.com/guide/mac-help/control-access-to-files-and-folders-on-mac-mchld5a35146/mac

"The latest version" doesn't mean anything, because there are two versions of Lightroom: Lightroom (desktop) and Lightroom Classic. So which one is it?