In the process of recreating exact copies of naturally generating structures block by block, I used structure voids to hold up gravel (and sand, anvils, etcetera). Working recently on my mineshaft, I updated a gravel block above the structure voids, and the whole patch fell down. I quickly confirmed that this happened consistently by attempting to re-place the gravel, and it is. I do not know how they are intended to interact, but I will assume that gravel's falling through is a bug, as it was the only way to hold gravel up with an invisible block that can be moved through. At no point in time did the gravel that was already falling stop to land on the structure void. Also, gravel falling onto a structure void on the ground will override the structure void, as opposed to dropping the item, as it has before.

The structure void blocks water, cannot be waterlogged, and can have torches, item frames, etcetera placed on it, so it does not act as a partial block; I see no reason why it should not hold up gravel.

I updated by tablet from 1.18.something directly to 1.19.10.23, but I was playing in a creative flat world that I've had for years and have never activated experimental features on this world.

I really need some way to float this gravel, as barriers are impossible to travel through and obstruct the passage of the structure I am copying (by hand, the ground around it is not filled in), and string is not present in the structure, so placing them down will also be extremely awkward and visually obtrusive.