Same issue in MC-266777 (Which found that i tested seen possible)

When non waterlogging copper grates, The skylight passes through them but if they were waterlogged doesn't passing lights.

Experimental features: yes

World Type: Overworld Infinite

Steps to reproduce

1. Create a new Infinite world with 1.21 Experiments
2. Locate to Sea/Ocean biomes
3. Place copper grates start at bottom to end of top in deep sea
4. Take bucket to remove waterlogged copper grates
5. wait for visible to dark brightness

Observed Result

The non waterlogged Copper Grates can allow skylight to pass through

Expected behaviour

non waterlogged Copper Grates can should not allow skylight to pass