I haven't seen this mentioned anywhere...
I was experiencing some glitchy freezing on my device, not wanting to perform a factory reset and lose data I tried a manual update instead, downloading the SWUPDATE.BIN file (6.8.2102) from Pocketbook support to my device and starting the upgrade.
I don't know if it's fixed the glitching/freezing I was experiencing...
BUT I now have dark-mode available! Bonus!
I'd recently checked for OTA updates and the system stated I already had the latest version despite not having dark mode available.