Linux

Been on Linux since 2007, so for me it's kind of the opposite. You just get settled with your OS after a while, you're used to how it works.

For me the immediately missing features is customizability in window management. I'm not a tiling fan, but I still miss basic convenience features like middle click paste, press alt and drag windows around or press alt and right click to resize windows from whichever side is the closest to the cursor. The different way it arranges windows (Linux tries hard to make them fit in unused space whereas Windows just opens it in the middle of the screen). Another big one is if you have a window focused and try to scroll another window in the background with your mouse cursor over it, it'll still scroll the focused window even though the mouse cursor isn't on it. Focus steal prevention is non-existent so if you're typing and another window pops open, it steals your keyboard input. The search bar is like, utterly useless, so is the Microsoft Store. The start menu doesn't open instantly like it has to load it every time. When you uninstall something there's still leftover crap of it everywhere.

Thankfully when it comes to Linux apps, their open nature means the majority of them just have Windows builds anyway, and what doesn't would work in WSL. So really all I can miss is the inherent flexibility and openness Linux gives me.