Sorry if this has been mentioned before, but I couldn't find anything and it bugs me, so here goes.
When holding an item (not a block or placable item) in your hand, the edges don't line up. That's about it. I'm pretty sure it started in 1.15.
To reproduce:
Take any item (again, not a block) and hold it in your hand.
It works best against bright blocks (I used sandstone in the screenshot).
Ignore the custom item, that's from a resource pack (which isn't the cause of this).
Thank you for your report!
However, we are already tracking this issue, and this report is a Duplicate of MC-73186, which is a report that has not been resolved yet.
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