Is it normal that I am seeing 3 entries in Disk Utility with only having 1 internal hard drive?

I have a 2021 MBP with a 500 Gb hard drive. In Disk Utility I am seeing the following entries:

Is this normal? Why is the same disk mounted in different locations, / and /System/Volumes/Data? And what is the unmounted disk?

Solution 1:

This is normal. The Macintosh HD volume contains files that do not need to change when macOS is executing, except during operations such as updates. This is what you selected in the first image. To prevent any changes from taking effect while macOS is normally executing, a snapshot is taken of the Macintosh HD volume. This is shown in the second image. Note, that the snapshot of the Macintosh HD volume is mounted instead of the current contents of the volume. The Macintosh HD - Data volume contains files that can change when macOS is executing. This is shown in the third image. All three volumes belong to the same APFS Volume Group. So while the Macintosh HD - Data volume is mount at /System/Volumes/Data, the volume also shares the / mount point with the snapshot of the Macintosh HD volume.

All of this seeming nonsense has to do with protecting data. You can read the following Apple documentation for more information.

Protecting data at multiple layers
What is a signed system volume?

I should also point out your Mac has an internal Solid State Drive (SSD) and not a Hard Disk Drive (HDD). Also this drive has hidden EFI, Preboot, Recovery and VM (Virtual Memory) volumes.