It didn't work for my device (Oasis 3). After reboot, the Display Cover option still does not show.
Code:
[root@kindle root]# cat /var/local/java/prefs/BookCover.preference
#User preferences for Book Cover Preferences
#Sun May 29 18:17:30 GMT-06:00 2022
BookCoversEnabled=false
isBCSettingAccessed=true
[root@kindle root]# sqlite3 /var/local/KWISClient.db
SQLite version 3.26.0 2018-12-01 12:34:55
Enter ".help" for usage hints.
sqlite> SELECT extra_identifier, experiment, treatment FROM main.experiments;
DecanterChromeV1|DECANTER_CHROME_V1_FALLBACK_328845|C
DecanterChromeV1|DECANTER_CHROME_V1_MALBEC_FALLBACK_370896|C
CuratorBookCovers|EREADER_CURATOR_BOOK_COVERS_307723|T2
sqlite> .exit
P.S. My Oasis 3 had removed ads already.