$WINDOWS.~BT and $WINDOWS.~WS folders help to downgrade Windows 10 operating system to the previous version of the new Windows version are causing problems. When any user tries to upgrade their Windows from Creators Update to Fall Creators update, such folders are created automatically with the files relating to the previous version of Windows installation. $WINDOWS.~WS and $WINDOWS.~BT folders are created when upgrading Windows from one version to another. What are $Windows.~BT and $Windows.~WS Folder
Go through this article, know the tricks to delete windows bt and also get to know about what are $WINDOWS.~WS and $WINDOWS.~BT folders.