"Announcing Windows 11 Insider Preview Build 26220.7271 (Dev & Beta Channels)"
Secondly, they're preloading the executable resident in memory to accelerate click to open, similar to what Chrome Browser does on Windows (and websites when browsing)
I don't perceive this as "fixing bad performance, given explorer has never been slow to open for me, but rather further optimizing the experience.
"We’re exploring preloading File Explorer in the background to help improve File Explorer launch performance. This shouldn’t be visible to you, outside of File Explorer hopefully launching faster when you need to use it. If you have the change, if needed there is an option you can uncheck to disable this called “Enable window preloading for faster launch times” in File Explorer’s Folder Options, under View. Looking forward to your feedback! If you do encounter any issues, please file them in the Feedback Hub under Files Folders and Online Storage > File Explorer Performance, or Files Folders and Online Storage > File Explorer."