When using a high res texture pack I get a big FPS drop if dropped items are nearby.   However CPU and GPU usage aren't very high.     I tried changing from 256 res textures down to 64 but it made no difference.   Doesn't affect all dropped items, eg dropped sugarcane drags me to to under 10fps but dropped dirt has no effect on FPS.

https://www.youtube.com/watch?v=qyK8JHfLFus

The PC is an Intel 9700k with RTX 3080.  It has the latest video card drivers.

I have also reported this to the texture pack maker.