Backup using
mariabackup --backup --target-dir F:\MD-Backup\ --user Buser --passsword XXX
successful
Prepare
mariabackup --prepare --target-dir F:\MDB_Backup\ --user Buser --password XXX
result
mariabackup based on MariaDB server 10.3.8-MariaDB Win64 (AMD64)
mariabackup: cd to F:\MDB_Backup\Restore\
mariabackup: This target seems to be not prepared yet.
mariabackup: using the following InnoDB configuration for recovery:
mariabackup: innodb_data_home_dir = .
mariabackup: innodb_data_file_path = ibdata1:10M:autoextend
mariabackup: innodb_log_group_home_dir = .
mariabackup: Starting InnoDB instance for recovery.
mariabackup: Using 104857600 bytes for buffer pool (set by --use-memory parameter)
2018-08-17 12:35:48 0 [Note] InnoDB: Mutexes and rw_locks use Windows interlocked functions
2018-08-17 12:35:48 0 [Note] InnoDB: Uses event mutexes
2018-08-17 12:35:48 0 [Note] InnoDB: Compressed tables use zlib 1.2.3
2018-08-17 12:35:48 0 [Note] InnoDB: Number of pools: 1
2018-08-17 12:35:48 0 [Note] InnoDB: Using SSE2 crc32 instructions
2018-08-17 12:35:48 0 [Note] InnoDB: Initializing buffer pool, total size = 100M, instances = 1, chunk size = 100M
2018-08-17 12:35:48 0 [Note] InnoDB: Completed initialization of buffer pool
2018-08-17 12:35:48 0 [Note] InnoDB: Starting crash recovery from checkpoint LSN=7388214
Last binlog file , position 0
180817 12:35:49 completed OK!

copy back
mariabackup --copy-back --datadir "C:\Program Files\MariaDB 10.3\data" --force-non-empty-directories --target-dir F:/MDB_Backup/Restore --user Buser --password XXX
copies back all files
copy back my.ini to target-dir.
start mysql service

C92012.err file attached.

datadir is C:\Program Files\MariaDB 10.3\data
table create uses DATA DIRECTORY='D:\C9/\data'
if DATA DIRECTORY='D:\C9/\data' is not used the service starts.