First, the default picture for any directory is a file folder (which is why it's incorrectly called a folder). Some apps modify the system to show a picture on the folder, but that's a flaky thing, and one update can destroy that, leaving you with the generic "folder" picture. (It's done at the operating system level - Linux - and apps aren't supposed to fool around down there.)
Originally Posted by
Iceysky twice where the phone ran out of batt & switched off on its own
That's a no-no - never allow the battery to get lower than 40%. Running totally out can kill a battery in a month if it keeps happening. (It's
very bad for the battery.)
are the display of the apps logo on their folders controlled in settings?
No. as I said, they're controlled in Linux. There is no "folder", there's just a directory (a file entry, but marked as "directory" instead of "link" or "file"), and Linux shows that, in its graphic interface, as a folder. It has no pictures for Facebook or WeChat, just for a folder. If Facebook or WeChat dig into the OS and capture its output to show different pictures for its folders ... they just shouldn't. (Doing things in Linux isn't something simple, like developing an app, it's playing with the operating system
while it's running. Something like looking for a gas leak with a lit match. If you're lucky, you'll find it. If not ...!!!)
