Thank you lazanet for this.

I was able to follow your instructions successfully on a PW5 on 5.14.1.1 with the UI reverted to the 5.13.6 style.
For some reason in addition to missing the dark mode toggle, I had two other settings that were absent, but can be reactivated using the same files.
To enable the "display book cover" option in the settings menu:
1) Create a file at /var/local/java/prefs/BookCover.preference containing the following:
Code:
#User preferences for Book Cover Preferences
#Sun May 29 18:17:30 GMT-06:00 2022
BookCoversEnabled=false
isBCSettingAccessed=true
2) And for `/var/local/KWISClient.db` insert this SQLite row:
Code:
INSERT INTO "main"."experiments" ("extra_identifier", "experiment", "treatment") VALUES ('CuratorBookCovers', 'EREADER_CURATOR_BOOK_COVERS_307723', 'T2');
To enable indicators for the last viewed locations in the pagenav, insert these three SQLite lines into KWISClient.db:
1) Ereader Unified Sync
Code:
INSERT INTO "main"."experiments" ("extra_identifier", "experiment", "treatment") VALUES ('EreaderUnifiedSync', 'EREADER_UNIFIED_SYNC_MILESTONE2_319553', 'C');
Code:
INSERT INTO "main"."experiments" ("extra_identifier", "experiment", "treatment") VALUES ('EreaderUnifiedSync', 'EREADER_UNIFIED_SYNC_MILESTONE1_308341', 'C');
2)Page Flip View
Code:
INSERT INTO "main"."experiments" ("extra_identifier", "experiment", "treatment") VALUES ('PageFlipViewDialogRevamp', 'PAGE_FLIP_VIEW_REVAMP_267001', 'T1');