MacOS – How to enable indexing for this internal HDD

I have a Mac running Mojave (10.14.6) with a new 2TB internal HDD with an APFS volume (called "Tár"). No matter what I try, I get "Indexing disabled" whenever I try running sudo mdutil -i on /Volumes/Tár/. All other volumes are indexing fine and the volume itself is working properly.

If I look at the Console after running the mdutil command, I see the following in the output:

mds nosymlink_mkdir() unable to realpath or parent paths do not match p:/Volumes/Tár/.Spotlight-V100: r:/Volumes/Tár:
mds Unable to create/find index location <private> 0

• There's no .metadata_never_index file anywhere.
• Trying to add the volume to the privacy excluded folders in Spotlight settings and then removing it doesn't help either.

What's wrong with this? How can I get this volume indexed?

edit:
diskutil list output:

$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *960.2 GB   disk0
   1:                        EFI NO NAME                 104.9 MB   disk0s1
   2:         Microsoft Reserved                         16.8 MB    disk0s2
   3:       Microsoft Basic Data Windows rendszer        314.6 GB   disk0s3
   4:       Microsoft Basic Data Közös                   645.0 GB   disk0s4
   5:           Windows Recovery                         530.6 MB   disk0s5

/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:                 Apple_APFS Container disk3         499.9 GB   disk1s2

/dev/disk2 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *2.0 TB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                 Apple_APFS Container disk4         2.0 TB     disk2s2

/dev/disk3 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +499.9 GB   disk3
                                 Physical Store disk1s2
   1:                APFS Volume macOS                   403.4 GB   disk3s1
   2:                APFS Volume Preboot                 45.3 MB    disk3s2
   3:                APFS Volume Recovery                510.4 MB   disk3s3
   4:                APFS Volume VM                      2.1 GB     disk3s4

/dev/disk4 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +2.0 TB     disk4
                                 Physical Store disk2s2
   1:                APFS Volume Tár                     179.2 GB   disk4s1

mount:

$ mount
/dev/disk3s1 on / (apfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
/dev/disk3s4 on /private/var/vm (apfs, local, noexec, journaled, noatime, nobrowse)
/dev/disk4s1 on /Volumes/Tár (apfs, local, journaled)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)
/dev/disk0s3 on /Volumes/Windows rendszer (ntfs, local, read-only, noowners)
/dev/disk0s4 on /Volumes/Közös (exfat, asynchronous, local, noowners)