The one that "helpfully" resets default applications and privacy settings to the ones Microsoft wants you to use, and then whines at you (or gives vague threats) when you do choose something else.
The one that turned logging in from pretty much an instant thing to a random wait while you get a "We're just setting things up for you" message on a pulsing background, and not-at-all-reassuring messages that "All your files are right where you left them".
It doesn't apply to anyone who's not eligible for that edition, isn't aware of it's existence, is just using the version that came with their device, or needs some specific feature in the 'Pro' variants (or whatever it's called now).
I remember having to bump up an edition from Home to get Bitlocker support for full-disk-encryption and something else.
e: While I've now migrated off Windows for a few years now, I still occasionally have to help family members who're wondering why X or Y no longer works, because MS decided to reset preferences.
As far as I can tell you have to go through an Academic Licensing service, which would immediately tell me to go away since I'm not a school/university/whatever.
It's simply not available to most people.
You used to be able to "disable fullscreen optimizations" in properties to get real exclusive fullscreen mode, but now you have to edit a registry entry for that binary, and even that doesn't work most of the time.
I have this beautiful 144hz monitor for a reason: latency sucks.
I should be able to launch windows every couple of months without having to wait so long to do anything that I forget why I even booted into windows in the first place.