The only thing Windows 10 UI rises to is a paragon of lagginess - and I say that about the UI I generally like, and one that runs on 10-year-old equipment just fine.
There's no good reason for a lag after hitting the "Start" button.
There's no good reason for a lag in the right-mouse-button context menu in Explorer (this was a "feature" since Windows 95, however).
I could go on for a long time, but let's just say that Win+R notepad is still the fastest way to start that program, because at least Win+R menu wasn't made pretty and slow (but still has history of some sorts).
The search box behaves in truly mysterious ways. All I want it to do is bring up a list of programs whose name contains the substring that I just typed. It's not a task that should take more than a screen refresh, much more so in 2019. And yet, I still have no clue what it actually does - if it works at all[1].
Want to give me fancy autocorrect? Fine. But first:
* Make a UI with instant feedback, which doesn't wait on your autocorrect
* Give me exact results instantly before your autocorrect kicks in
* Run your fancy slow stuff in the background if resources are available
* Update results when you get them... if I didn't hit "enter" and got away from you before that.
It's not that complicated. We've got the technology.
And also, there's still no fucking reason a USB keyboard/mouse should be more laggy than their counterparts back in the day.