Steps to Reproduce:
Create a world with a PBR enabled resource pack and the "Render Dragon Features for Creators" experiment enabled;
In first person view, look at the ground and observe your shadow;
Grab any block or item.
Observed Results:
With the exception of attachables, any block or item that you hold will make zero changes to the shape of your shadow.
Expected Results:
Any held block or item casts the appropriate shadow.
Notes: Similar to MCPE-177190, but affects every block and is only applicable in first person.
Can confirm, affects 1.20.80.21.