I was bitten by an iOS 14 bug while fiddling with Home screen widgets for an article. I don’t know quite what triggered it—perhaps moving a large Weather widget over a Home screen that was entirely filled with folders—but the end result was that about half of my folders were deleted, and the apps inside them promoted to being on new Home screens.
Needless to say, I wasn’t very happy about this. My best advice for the moment is to avoid putting Home screen widgets on screens with folders. Perhaps put the widget on a screen and then add the folders later, if that’s what you want.
I haven’t reported this to Apple yet because it’s just a one-off situation, but it’s the sort of thing we can hope will be fixed in an update.