[OnePlus 10 Pro] dlads:
1. it's more then likely apps, follow my tips at the end of this message.

2. That depends, apps is the main cause for concern, again follow my tips.

3. You should always be using oxygen updater to obtain full firmwares... This sentiment is doubled if you're rooted.

Tips:

Change 5G to 4G

Remove tiktok is 100% dodgy Chinese spyware.

Remove Facebook use web based

Remove Facebook messenger use web based

Remove Twitter use web based

Remove any ad based apps pay for the pro version

Turn off gestures like lift to wake

Change from QHD to FHD (No difference)

Allow auto brightness

Turn off WiFi overnight

Turn all updates to manual not auto (play store)

Remove any so you don't use

Change back up to once a month (WhatsApp)

Turn off location history (Google)

Use titanium to remove any system apps you don't need

Don't allow anonymous usage statistics for any app ever.

Don't allow tracking cookies on any website

Use adaway (root needed)

Don't open web pages in Google app (I use Samsung browser)

Don't use xposed.

If you game you will not get high SOT scores, period.

Don't bother with battery saving apps or monitoring apps.

Streamline your apps, if you don't use it, remove it.

Don't allow WiFi scanning (as in letting other apps use it when it's not on)

Never allow personalised ads.

Never allow notifications from websites

Always decline cookies unless your absolutely have to allow some tracking (common sense prevails here)

Optimise as many apps as possible unless it affects performance.

Don't allow apps to remain open in the notification area.

Change your launcher, my preferred launcher is lawn chair and this did actually burn up some battery when compared to the OnePlus launcher.

Don't use live widgets (yes they look cool, but they annihilate your battery)

Live wallpaper, again very cool, but battery burners.

Again! Don't charge overnight, make a note of your percentage then see what it is in the morning, you shouldn't be losing more than 5% really, if you've done well then it'll be reflected here, the good SOT results will follow.

Turn off live read outs of network speed, RAM usage in the status bar.

Turn off NFC unless in use.

Leave location on in quick settings.

Don't overcharge your phone, IE: overnight

Don't allow your phone to fully deplete the battery.

Whatever anyone says, this does 100% damage batteries, there is no argument here and I won't entertain anyone who says otherwise, Ive seen through real life tests what this results in, bloated, inefficient, possibly dangerous lithium batteries.

Keep your phone out the sun.

Keep it out of extreme cold.

Keep your device clean dust free.

Snapchat, Viber, house party, apps like that tends to use more battery as they don't have great dormancy periods.

Apps like speed test by Ookla tend to have location tracking, similarly they tend to turn themselves on and off when they feel like it, my advice, install test and uninstall.

Allow a couple of battery cycles between tweaking sets, to give you an idea of how much of a difference you've made.

Use BBS to see what is being used, once you've removed problems, remove BBS.

I've just written this from the top of my head so o probably missed some things, the general idea is to keep your device clean and fresh, remove files you don't need any more.

Keep an eye on apps that misbehave or aren't wanted, index your folders so they aren't a mess.

The more good things you do means the more potentially bad apps you can have on your phone, eg if you really need Facebook, you could keep it so long as you clean up other areas of your phone.

Good luck.