Macintosh HD volume and Macintosh HD - Data

Ideally you should perform a clean install of macOS by first erasing the physical drive (Intel Mac only -- different for an M1 Mac) before installing macOS so you have a clean factory fresh install of macOS without any nasty surprises that may have been left behind by the previous owner. Within Disk Utility you may need to click "View" and select "Show All Devices" so that the physical drive appears on the left pane of Disk Utility. Here is an Apple article describing what the previous owner should have done prior to selling the Mac (you can only do the last step):

What to do before you sell, give away, or trade in your Mac - Apple Support

Of course a clean install destroys all data on the computer so you need to make sure to have a backup of your data before erasing the drive for the clean install.

I'm now confused at which Data volume you removed.

The one you show in the screenshot (Macintosh HD - Gegevens) is the orphan left behind (previous owner's).

If you disclose the caret (>), you should see a Data volume inside that volume group.

When you view the Macintosh HD in the Finder, Finder makes it look like it is one single volume. The Data volume is mounted to /System/Volumes/Data.

If you select the orphaned Data volume in Disk Utility, you will see the mount point (Activeringspunt) as /Volumes.

Remove the orphan in Disk Utility by selecting it and clicking the Remove Volume button (–).

Big Sur and Later splits the drive into several system volumes and a Data volume.

What you see in the screenshots are the System Volume (gray), it's sealed Snapshot, and your Data volume.

The data volume you removed was from the previous owner.

You don't need to remove your Data volume. I became confused because I couldn't tell which Data volume you removed as the only screenshot showed the previous owner's data volume.

It's possible it merged in the previous owner's data. Check for a home folder in /Users/

You can delete that.

That should be fine. You only removed the other owners data drive. Yours appears to be there.

The old Data volume was (or will be) removed. There is nothing more that needs to be done.

Nothing could have modified the System Volume, and the OP reinstalled the OS over the top.