Macintosh SSD and Macintosh SSD Data drive?

The natural aspect of these system parts is that usually in normal use

you would not see them on the desktop. Otherwise they're normal!

• Why macOS Catalina installer splits data and system folders - idownload

https://www.idownloadblog.com/2019/10/24/macos-catalina-hidden-volume/

• System volume: This read-only volume contains all the operating system files that should never change during use of your computer.
• Data volume: This volume contains everything else, including your home folders such as Documents, Music and Movies.

Apple itself states:

Catalina

runs in a dedicated, read-only volume — meaning it’s completely

separate from all other data and nothing can overwrite your critical

operating system files.

There may easier to understand Support articles that explain this better.

While that said, my newest 'macOS Mojave 10.14.6' does OK, as it is!

If you are running Catalina on an SSD, then the drive is formatted APFS. As such, APFS creates a space on the drive called a "container." The container has five volumes within it. They are as follows:

Macintosh SSD - visible and mounts on the Desktop

Macintosh SSD - Data - invisible but mounted

Preboot - invisible

Recovery - invisible and the equivalent of the Recovery HD

PM - invisible

The Data drive should not be visible on your Desktop. If you open Disk Utility and change the View dropdown menu to Show all devices, then you will see the basic structure of the container and the first two volumes. If you see two Data volumes, then the configuration has been corrupted.

You cannot stop this because it's integral to an APFS formatted startup disk. You are damaging the configuration by not knowing what you are doing or why. You should learn to ask before doing something you don't know about rather than after the fact.

I think that now you should start over from scratch. After reinstalling Catalina, please do not mess with the drive configuration.