I used to go a day charging my phone just twice. After the update, One Ul version: 5.1
Current version: G990BXXS3EWC4/
G990BOXM3EWC4 / G990BXXS3EWC4, I have to charge my phone more than 4 times in a day even with reduced usage. I don't think it's a reduced battery power as I've used this phone for only exactly a year now
How many vampire apps are running as they love battery's. Also do you have adaptive lighting running as turning it over to manual and setting the brightness to what is comfortable to you will save the battery. Darkness and extra dim also help. Wifi and Bluetooth, if not required turn them off as they will search for signals.
You can try clearing the cache and storage data in the device health services app and device care app to reset the battery stats to see if that helps. You can also add apps to deep sleep, sleeping or never sleep under background usage limits.