Clear it in 3 steps
Start the environment
Investigate the target
Submit the flag

Analyze `mft_records.txt`, a dump of the NTFS Master File Table, to recover information about deleted files. A NOT_ALLOCATED (deleted) record whose resident $DATA was not overwritten still contains the flag.
Isolate the NOT_ALLOCATED (deleted) records from mft_records.txt
A deleted-but-not-overwritten resident ($DATA) file still holds its content
The flag is in that single record's resident data (TextPreview)