You're getting some plugin-related errors, so start by disabling all plugins, restarting Zotero, and resetting translators from the Advanced → Files and Folders section of the Zotero settings. Then make sure your Quick Copy setting is set to an existing translator or style in the Export pane of the settings. Then try again.

Are you dragging between two regular collections?

In other words, you're not dragging out of or into My Library or some other special collection?

When exactly are you pressing and releasing Shift?

Right, so you're dragging from My Library, not a collection. All items are always in My Library, so you can't move something out of it. Zotero has always worked this way.

https://www.zotero.org/support/collections_and_tags#the_zotero_collections_model

Yes. I'm not sure why you're asking? Just try it. It should work fine. That's just not what you're actually doing in the video you shared.

It's about the actual view that you're in when trying to drag. You were in My Library, not any other collection, and you can't move from there, because items always exist in My Library.

It sounds like you maybe expect moving from My Library to move the item out of all other collections it's in, but moving doesn't work that way and never has. Moving is for moving an item from one collection that you're in at that moment to another collection. It has nothing to do with any other collections the item might be in.

But with Zotero 7, you can easily remove an item from collections from the item pane, as you did yourself in the video. So if you want to remove the item from all other collections, you can just do it from there.

I can't really explain it more clearly than my comment above.

If you want to share another video that shows this not working when dragging from one collection to another, you can do so, but that's not what you showed.

Again, you were in My Library, not a collection, at least in the video you shared.

Because My Library is selected in the collections pane on the left.

Again, the fact that the item has been added to some other collection is totally irrelevant.

I think we're done here. You seem to just be fundamentally misunderstanding how Zotero works, but nothing about this is new in Zotero 7. If you're not having a problem now, we don't need to continue here.