161gb not appearing on diskutil after deleting second OSX partition

After a lot of back and forth in comments, it’s looking like you have a couple containers that won’t collapse back into one chunk of space, so you’ll want to live with this until such time as you make a backup, wipe the APFS containers, recreate one container and then re-make all your volumes in one APFS container and reinstall the OS / restore the data from backup.

I'm thinking you added a partition when you just needed to add a volume to the same container so all the volumes could share free space and not block each other from using the full free space:

enter image description here

If you clicked Add Volume you would only have one container and the Untitled2 volume would be quick and easy to delete and not take any space away from the other volumes in the same container.

bootable volume - slim

Untitled2 volume

$ diskutil list
/dev/disk0 (internal):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                         251.0 GB   disk0
   1:                        EFI EFI                     314.6 MB   disk0s1
   2:                 Apple_APFS Container disk1         250.0 GB   disk0s2

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +250.0 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume slim                    199.5 GB   disk1s1
   2:                APFS Volume Preboot                 65.5 MB    disk1s2
   3:                APFS Volume Recovery                1.0 GB     disk1s3
   4:                APFS Volume VM                      2.1 GB     disk1s4
   5:                APFS Volume Untitled2               647.2 KB   disk1s5

In your case - the parts of disk0 are mutually exclusive and the disk0s3 is locking away 167.6 GB of space from the main container.

In my case, you can see that both volumes see the same amount of free space and you'll not have that flexibility since you have two high level "Containers" that can't share free space.

System Information storage view from the About This Mac storage pane