I have a Pixel 8 Pro running GrapheneOS and, since last year with a Pixel 6a, I have been noticing that the "screen time since last full charge" thing always shows "0 minutes" even after I've been using the device for hours. I also kinda remember it started happening when the Android 14 port came out last year, when I still had the Pixel 6a as main phone.
Don't know if it is some upstream AOSP/Pixel bug or if it is related to the battery saver option being enabled or if I have disabled background usage for some app that I shouldn't have disabled. But I don't think it is caused by nothing I did, because I had factory reset GrapheneOS on the Pixel 6a (as it still not my main phone anymore) and the issue still happens.
Also, I don't know if it could be related, but I had a Galaxy S20+ a few years ago and I used/use its PD charger on the Pixel 6a and now on the new Pixel 8 Pro. Could this charger be damaged from little accidents over time and now damaging the functioning of the devices batteries, including messing with the screen time counter somehow?
By the way, I also noticed that when I charge the Pixel 8 Pro with the phone powered off and using this charger, it boots into the OS instead of charging powered off, while another Motorola PD charger I have at home charges the phone normally when the phone is powered off.
PS. Let me know if I tagged the wrong tag/category for this post.