How do I remove "Other Volumes in Container"

If you have adequate backups you can erase/ reinitialize/partition the parent drive and reinstall the macOS, then restore your data.

If you have no backups of your data, there may be some Terminal tricker to recover from your situation.

Open Terminal, run this command & report the output...

diskutil list

/dev/disk0 (internal, physical):

   #:                       TYPE NAME                    SIZE       IDENTIFIER

   0:      GUID_partition_scheme                        *500.1 GB   disk0

   1:                        EFI EFI                     209.7 MB   disk0s1

   2:                  Apple_HFS Macintosh HD            499.2 GB   disk0s2

   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

According to Apple: “With Apple File System [APFS], the disk space of a container is shared among all of its volumes…. Space Sharing allows multiple file systems to share the same underlying free space on a physical volume [disk]. Unlike rigid partitioning schemes that pre-allocate a fixed amount of space for each file system, APFS-formatted volumes can grow and shrink without volume repartitioning.”

https://www.macobserver.com/tips/deep-dive/apfs-faq-partitions-volumes-afps-containers/

A drive formatted to use APFS can have multiple containers. Each container can have multiple volumes, and the volumes within a container share the space within their container. You can add additional containers in order to isolate one group of volumes from another and prevent volumes from sharing space. This is done by partitioning the APFS drive.

https://blog.macsales.com/44596-partition-drives-create-apfs-containers-for-space-sharing-with-disk-utility

This seems to be what I get:

https://discussions.apple.com/content/attachment/a690bc0d-d8db-4061-98f7-315c8a435fb3

I would be curious to what you did to get into this situation?

Something is not right there— the container should be nearly the size of the drive in a generic format.

The Macintosh volume is what you have used up.

 diskutil list

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *480.1 GB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_APFS Container disk1 479.9 GB disk0s2

/dev/disk1 (synthesized):

#: TYPE NAME SIZE IDENTIFIER

0: APFS Container Scheme - +479.9 GB disk1

Physical Store disk0s2

1: APFS Volume Macintosh HD 326.0 GB disk1s1

2: APFS Volume Preboot 22.6 MB disk1s2

3: APFS Volume Recovery 516.6 MB disk1s3

4: APFS Volume VM 2.1 GB disk1s4

:)