Since the introduction of macOS 10.15 Catalina and above
Apple introduced a Macintosh HD Volume ( not partition ) which is Read Only
They also brought about a Macintosh HD-Data Volume which is where your User Account is kept
This is totally normal and when you and I look at the Drive it would appear as One.
Starting in macOS 11 and above
Apple went even further in regards to the MacIntosh HD Volume and made it both Read Only and Sealed
Not to cause confusion but to see a more detailed view of the Drive Structures
You may consider using Disk Utilities
To illustrate this reference the image below
This image is from an Apple Silicon computer running macOS 15.5 Sequoia some it may look different than an Intel Computer
