Yeah, I have a newer revision of Libra, I checked that using Terminal in KOReader when I bought the device.
And what is a "factory firmware" on my device should be newer than 4.34.20097 (as 20148 > 20097, and October vs September).
I didn't let it connect to WiFi after doing the "manual factory reset" so it couldn't download and install any updates
But yeah, when I unboxed the device in 15th of December 2023 I registered and logged into a Kobo account and to do that I had to connect to WiFi and thus it instantly proceeded to download and install 4.38 without asking me anything
So I that was what I was using.
Now as a last-ditch effort I've tried to see if the factory reset itself + downgrade back to what was initial firmware out of the box will have any impact on battery life.
Not really holding my breath for that.. this is how the device worked since the day 1, and I didn't do anything special with it (added 1 epub & 1 kepub to compare stock firmware, then proceeded to "install" KOReader and I've been mainly using that, stock software I've used only for the purposes of comparing battery drain) after it auto-updated to the latest firmware.
And even now when I've charged it today (in preparation to doing factory reset) I noticed that in like 2 minutes time from supposedly 88% full to 97% full. The battery indicator is clearly not that reliable...