This week's Windows Update has made almost everything on my PC launch much more slowly.

MS Office and various other programs take up to 10 seconds to open where they used to take barely 2. Notepad -- arguably the simplest program in Windows -- takes at least 8 seconds to appear. Even just opening ordinary JPGs takes 10 seconds vs. <1 second last week. And batch files of 20 or so lines (doing simple stuff like SUBSTing drives or copying a dozen non-huge files), that used to finish in a flash, now take several seconds per line.

I'm assuming the root cause is Windows and not a security program or other culprit, because if I restore the system to March 1 (build 10586.104) everything is fast again. Of course then Windows notices this and forces a re-update within a day or so, and the PC is like a drunk uncle again. The only launch action that doesn't seem affected is opening a folder from a shortcut; that happens instantly -- although, if this is a clue, a few shortcuts to c:\windows\explorer.exe + folderpath take much longer. (I can't explain why I had those in the first place, but the launch-time difference between them and a simpler shortcut to the same folder was startling.)

I should stress that, except for batch files, most programs run fine once they're open. And I haven't tweaked my AV to do anything different at program launches.

My job requires lots of quick access to lots of programs and files, so I can't work like this. Why is this happening and how can I stop it?

This is Windows 10 Pro 64bit with 12GB RAM on a 4-year-old Dell desktop with gobs of free hard drive space. I upgraded from Win7 in November, and while it wasn't a pristine wipe-and-install it's performed quite well until just now.

Sincerely grateful for any clues.