How to delete a partition without losing data.

Looks like you did it myFriend. :)

disk5 is generally the 5th Disk seen by the OS.

Containers is what APFS uses pretty much in place of the old Partitions, a container does hold a set size like a old partition does, all the free space is available to any other APFS "partition", they just use it as needed.

Shaded part is used amount.

In Finder how much free space does a Get Info say you have?

You can use this command in Terminal to see...

im19% diskutil list

/dev/disk0 (internal, physical):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme            *1.0 TB   disk0

  1:            EFI EFI           209.7 MB  disk0s1

  2:         Apple_APFS Container disk4     1000.0 GB disk0s2

/dev/disk1 (external):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme             1.9 TB   disk1

  1:            EFI EFI           314.6 MB  disk1s1

  2:         Apple_HFS SSD2          1.9 TB   disk1s2

/dev/disk2 (internal):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme             28.0 GB  disk2

  1:            EFI EFI           314.6 MB  disk2s1

  2:         Apple_APFS Container disk4     27.6 GB  disk2s2

/dev/disk3 (external):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme             1.9 TB   disk3

  1:            EFI             209.7 MB  disk3s1

  2:         Apple_APFS Container disk5     1.9 TB   disk3s2

/dev/disk4 (synthesized):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   APFS Container Scheme -           +1.0 TB   disk4

                 Physical Stores disk2s2, disk0s2

  1:        APFS Volume Macintosh HD      11.3 GB  disk4s1

  2:        APFS Volume Macintosh HD - Data   655.3 GB  disk4s2

  3:        APFS Volume Preboot         84.5 MB  disk4s3

  4:        APFS Volume Recovery        529.0 MB  disk4s4

  5:        APFS Volume VM           2.1 GB   disk4s5

/dev/disk5 (synthesized):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   APFS Container Scheme -           +1.9 TB   disk5

                 Physical Store disk3s2

  1:        APFS Volume SSD3 - Data       720.8 GB  disk5s1

  2:        APFS Volume Preboot         402.1 MB  disk5s2

  3:        APFS Volume Recovery        626.4 MB  disk5s3

  4:        APFS Volume VM           17.2 GB  disk5s4

  5:        APFS Volume             15.3 GB  disk5s5

  6:        APFS Volume Update         1.9 MB   disk5s6

/dev/disk6 (external, physical):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme            *500.1 GB  disk6

  1:            EFI EFI           209.7 MB  disk6s1

  2:         Apple_APFS Container disk8     499.2 GB  disk6s2

  3:         Apple_Boot Recovery HD       650.0 MB  disk6s3

/dev/disk7 (external, physical):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme            *2.0 TB   disk7

  1:            EFI EFI           209.7 MB  disk7s1

  2:         Apple_HFS 10136          2.0 TB   disk7s2

  3:         Apple_Boot Recovery HD       650.0 MB  disk7s3

/dev/disk8 (synthesized):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   APFS Container Scheme -           +499.2 GB  disk8

                 Physical Store disk6s2

  1:        APFS Volume Monty - Data      40.2 GB  disk8s1

  2:        APFS Volume Update         753.7 KB  disk8s2

  3:        APFS Volume             15.7 GB  disk8s3

  4:        APFS Volume Preboot         300.8 MB  disk8s4

  5:        APFS Volume Recovery        1.1 GB   disk8s5

  6:        APFS Volume VM           1.1 GB   disk8s6

/dev/disk9 (disk image):

  #:            TYPE NAME          SIZE    IDENTIFIER

  0:   GUID_partition_scheme            +126.2 MB  disk9

  1:         Apple_HFS audacity-macos-3.1.3... 126.2 MB  disk9s1

im19% 

You're welcome my friend, glad I could help. :)

Yes the Get info deal should work.