Mac OS Catalina New Folder on File Menu Greyed Out

After Mac OS Catalina was released I created multiple "containers" on my hard drive. One container is running my old OS "Mojave" and another I installed a fresh copy of "Catalina".

The purpose of this was so I could start transitioning over to "Catalina" and I could still run any old 32-bit applications under the older "Mojave" version.

The problem I am experiencing is that "New Folder" is greyed out on the Finder when running Mac OS Catalina. So I cannot create any new folders while using the Finder on "Macintosh HD" hard drive.

I did hear about the new Catalina version creating two separate hard drives. One, the "Macintosh HD" which houses the Mac OS and is read-only. And the other being "Macintosh HD - Data" which is "supposed" to be the drive where everything is able to be written to. As far as I am to understand though the two hard drives appear as one on Catalina. While running Catalina I only see the one hard drive "Macintosh HD" on the screen but I cannot create any new folders on that drive from the Finder.

If I boot off my Mac OS Mojave container I can see the "Macintosh HD" container in the Finder as well as the "Macintosh HD - Data" container and the container that contains the Mac OS Mojave. This way I could create a new folder on the "Macintosh HD - Data" container if I wanted to. But I shouldn't need to go this route just to create a new folder on the Catalina drive.

Should I just erase the Catalina container and install another fresh copy or is there something I need to do to be able to create new folders on the main part of the hard drive while running Mac OS Catalina normally?

Thanks for anyone's advice. I am running Mac OS Catalina on a "Mac Book Pro (Retina, 15-inch, Late 2013)" with macOS Mojave 10.14.6 in one container and macOS Catalina 10.15.2 in the other.