I'll go first: r/kitty. One of the hundred grillion cat subs back on Reddit, the culture in this one was you posted a cat picture, and the only word allowed in the title or in any comments or replies was "Kitty."
Someone is using that subreddit for covert communications, I just know it. Either on the level of "if u/PM_me_your_nostrils posts an orange cat, we attack at dawn!" or there's some steganography going on with the pictures, but that subreddit was too stupid to be as active as it was.
Windows, Android, & Apple software used to nag you about installing updates endlessly. They don't do that so much anymore. I think it's because instead of alerts asking us to install updates, they now create network outages, software crashes, and other minor issues that require a restart. How often do you have some inexplicable problem, restart your device to fix it, and your machine is like "Hey while we're in there we're also installing this update we just downloaded a moment ago."
The number of updates I've seen on my phone has decreased because it's old enough to be done with feature updates. I got out of Windows before it got that bad.
Something I don't miss from Windows was each app was responsible for its own updates, so you'd sit down to draw something in CAD or whatever and it would say "need to update to continue" so you'd have to sit there listening to the fans whine for a few minutes before you could start. This still happens occasionally on Linux because some software is just the Windows version running in some compatibility layer or something, but it happens a lot less because the package manager handles all that at once.