I've found with the same world and same settings with 8 chunks, Vanilla 1.19.4 gain almost 500+ fps.
But after I installed Fabric+API, there's only 300 fps.
So I guess 1.19.4 FAPI might break sth. Please test more about it.

Now I tested with No API and other mods. Performance Drop still.
I'm using Zulu JDK 17.0.5

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