In Windows 10 Build 1903, Microsoft has enabled the “Launch folder windows in a separate process” option by default. This causes each folder you open in File Explorer to use its own process, and if one hangs, it does not affect the rest of the open folders or the desktop. […]

from https://www.bleepingcomputer.com/news/microsoft/windows-10-build-1903-opens-folders-in-their-own-process-by-default/