I ran a couple of searches to see if this is already reported, but couldn't find any specifically addressing this (found a few for the weird shadow issue, but not this one.)
Shadows on items used to rotate (I think) with the item, but are now static. In addition (and I'm not sure if this was ever different than how it is now) The shadow for everything is a square, even "flat" items.
To reproduce, throw an item onto the ground.
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kumasasa
The items do not rotate...
....anymore, items in fancy mode should rotate, and in fast mode should rotate to face your view.
However, the shadow never did rotate, likely because shadows in default are circular, not gaining any benefit from rotation, they would likely not add it. The shadow being square is due to the resource pack you're using.
So this isn't really a dupe, but a separate issue and feature request.