Background process doing some sort of migration or other data conversion between versions? Strange the device wouldn't wait until during the night while plugged in, but without context, that might not be an option.

Kind of sad that we don't have a top or process viewer. Or free -m / open system. This makes me yearn for an open source OS on my phone again, I may have to look into a pine phone.

If you connect your iPhone to your Mac you can run Instruments on it to figure out what is going on. I used to recently to figure out that Slack had been making my entire phone slow because it was busy looping in the background.

I agree, but it shouldn't be a classic process viewer. It should be a task viewer which has some context or understandable description. Like "photo analysis job" or "iOS 14.5.1 data migration job".

Yes... I remember back in the day I had terminal with root access on a jailbroken iPhone. You could install almost any package on your phone via terminal.

Stick a fan in it so I can hear if a background process is being run!

Might explain why my battery dropped that much, too.

One of iOS' more annoying quirks is its opacity and lack of user affordances.

The volume buttons don't seem to affect haptic noises, but the mute button does. The OS locks up for about a minute when you change passcodes while it re-crypts everything, but from the user's perspective it just looks frozen. The implications of opting into their 'find my...' and iCloud networks are not adequately explained. The devices take 15-30 seconds to actually cut power after they appear to shut down, and during that time they won't respond to any button presses.

The list goes on, using a modern iPhone feels like you are constantly negotiating with a disingenuous UI. The OS regularly claims to be done with something while it continues working furiously in the background, and it is full of undocumented exceptions to common settings.

Indexing or rebuilding I guess.

Yet no notification. The goblins inside the ios doing their thing behind closed doors.

Even a heads-up saying "hey we're doing some work behind the scenes on your device as part of the upgrade" would do.

Is there mention of this in any of the dialogs that one is asked to click "I have read and understand" that were not actually read? I remember Photos telling me that it was scanning the library to do their new layout after whatever update that was. That was to that specific app, and not a system wide notification, but it also said it would be paused until it was plugged in.

I could see a new something in the Settings that indicates post-OS upgrade showing migration status being useful.

If there was I didn't see it. But that is no surprise. Its not a way for them to escape a notification either imo. Especially if its slowing everything down.

That's potentially a good idea. It could even be hidden in the developer section, since those are the people most likely to notice.

Yeah pretty sure it’s this. Have seen various complaints about both macOS and iOS sluggish performance post upgrade to end up being just temporary while caches / indexes rebuilt, file systems migrated etc

Likely, yes. The thing is, the phone does not "heat up". Perhaps they throttle the whole phone down globally and let the background update processes run at a slow speed/low priority so they don't heat up the phone too much.