Did you toggle on Night Light?
Settings > Display > Night Light
If not, please explain what you see in more detail.
Battery Saver mode disables screen animations and dims the screen.
Did you enable developer options, and disable screen animations there?
If so, turn off developer mode, or adjust to your preferences.
- A soft reset by press and hold the volume-up and power button simultaneously until the phone restarts may sort out all sorts of strange issues.
- A too slow or defective SD memory card spoils everything.
I would not do a factory reset yet, the phone is faster without animations.
Instead I suggest clear the cache of battery related system apps. It's just a wild guess, since I can't replicate the issue - and I don't know exactly what you see on your phone.
The procedure does not delete any user data or settings, but it vacuum cleans any leftover bugs from the update:
Settings > Apps & notifications > App info
Tap the menu dots top/right and select Show system
Scroll to Battery protection, tap and select Storage, tap Clear cache
Go back to All apps, scroll and clear the cache of Power saver and PowerMonitor in the same way.
- Clear the cache of the Camera app also, to make sure that panorama mode works after the Oreo update.
Do a soft reset afterwards by press and hold volume-up and power.
If still unresolved, try restart the phone in Safe mode: Press and hold the restart option in the shutdown options > tap restart in safe mode.
Screen animations are enabled in safe mode, and it should rule out any third-party apps interfering with screen.
Using the phone in safe mode for a couple of hours, then restart to normal mode can sometimes sort out strange issues.
Please let us know how it goes?