Discrepancy between folder size at rest compared to when I go to copy it on Windows 10

Where exactly does it show '11Gb' - can you post a screenshot where it shows both Size as well as Size on Disk?

Before the copying starts, are you asked for your consent (elevation) on a user account control dialogue? That would be an explanation, since the normal properties call will only count folders that are accessible without elevating.

>>Where exactly does it show '11Gb' - can you post a screenshot where it shows both Size as well as Size on Disk?

If I right click on the file and then select "properties"

>>Before the copying starts, are you asked for your consent (elevation) on a user account control dialogue?

no, not asked for elevated privileges.

Is the folder shared on the mac that you are copying Into windows
If mot mistaken, mac files have biforkayed files. Data and resource ....

What does the space report when checked from the macos?

You forgot to mention Size on Disk

I would try to determine which one is right, 11 GB or >30GB.
Download the freeware treesize, execute it elevated and have it show you the folder size.

Unix style systems use a lot of symlinks.  You are likely copying the file and the linked folders.  If you want to do it correctly, you should do it from the command line with rsnyc.