I'm not sure there even is a good place where programs can store their internal system files without requiring root other than mixed in with the user Home.
/var/run/user/<uid>/ ?
Or what do you mean?
> On iOS/iPadOS nothing happens other than not having the documents you saved in there.
That is, frankly, a ridiculous test for the issue under discussion. Even if everything was stored under a top-level subdirectory set aside for application data in a perfectly orderly way, nuking $HOME would still break things.
Besides all that, hidden directories in the root of ~ are conventional¹ places to store application config files and so on, and can't be mistaken for conventional places to store documents. On most Linux-based operating systems, the conventional place to store documents is (obviously) ~/Documents, which is created ahead of time for all users. That folder doesn't generally end up polluted with things that aren't documents.
> On iOS/iPadOS nothing happens other than not having the documents you saved in there.
If you delete /var/mobile or any of the things that $HOME points to in the context of some app, you'll definitely lose app settings.
The app sandboxing on iOS does something nice by sort of forcing app configuration data to live within conventional directories, but none of that is captured in the "what if you delete ~" test. (The fact that $HOME isn't really directly exposed to the user sort of does; the local files you're comparing to $HOME on Linux are actually $HOME/Media on iOS.)
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1: https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch03s08.htm...
Never have been different. What did your relatives doing?
There were cases where phones were not consistent. Pictures from the camera, or saved from MMS, or saved from the Web, or screenshots, did not all go in the same place. Just like you would have on a desktop :) I don't remember that well the pre-2010 android, but it had some issues too.
Even to this day, WhatsApp saves photos to the gallery, but in its own album. At least on iOS those are part of the regular gallery so you'll always find them (an album is just a "tag" on the photo). Android has a dedicated album too, but the picture set is distinct from the main picture gallery. So are screenshots. That's more control and power, but utterly confusing for older people. Younger relatives are fine, older fail to navigate around this and find "the picture your auntie sent to me through whatsapp". Yup, it's there, but not in the main camera roll.
This is what I mean by "you know where the pictures are going".
PS: Apple botched the UX of the gallery app in the last two iOS versions so much that even I, a young tech-inclined person, loses my way around. So do my relatives. They're sorta catching up /s
