mariabackup restore looking for folder that doesn't exist

Trying to use mariabackup to migrate a database from Windows to Linux:

On the source server (mariabackup based on MariaDB server 10.4.11-MariaDB Win64 (AMD64))

mariabackup --backup --target-dir=e:\mbk --user=user --password=thepassword
mariabackup --prepare --target-dir=e:\mbk

I copy the backup to the destination system (mariabackup based on MariaDB server 10.4.22-MariaDB Linux (x86_64))

mariabackup --copy-back --target-dir=/var/lib/mysql

mariabackup based on MariaDB server 10.4.22-MariaDB Linux (x86_64)
2021-12-22 11:21:28 0 [ERROR] InnoDB: Operating system error number 2 in a file operation.
2021-12-22 11:21:28 0 [ERROR] InnoDB: The error means the system cannot find the path specified.
[01] 2021-12-22 11:21:28 error: cannot open file ibdata1
[01] 2021-12-22 11:21:28 Error: copy_file() failed.

If I run mariabackup --copy-back without a target-dir specified it does this which is totally unexpected:

mariabackup --copy-back
mariabackup based on MariaDB server 10.4.22-MariaDB Linux (x86_64)
mariabackup: Can't change dir to '/mbkagain/mbk/xtrabackup_backupfiles/' (errno: 2 "No such file or directory")
[00] 2021-12-22 11:22:26 Can't my_setwd /mbkagain/mbk/xtrabackup_backupfiles/

I suspect the reason that it cannot find the files in xtrabackup_backupfiles is because there is no xtrabackup_backupfiles folder created on the source server....(???)

Does anybody know why the Windows version of mariabackup doesn't create the xtrabackup_backupfiles folder or why the Linux version expects that it will?

Which one is "incorrect"?