An open tank as you described as an “open glass lobster tank” is probably the best option for specifically a flowerhorn. As a few days ago he only had 2 small caves inside her tank and messaged me with pictures of his flowehorn with his kok scraped up. Even lost scales. You can keep your flowerhorns with decor all you would like. Do I personally think it’s the best way? No. I feel flowerhorns are a trophy fish. Not as in a rare fish, but as a fish that will win competitions. A flowerhorn with less decor to no decor and no gravel will have significantly better look and health. It is a win win for the flowerhorn and the owner. As the owner have less to clean and the flowerhorn will stay healthy.Not sure how an open glass lobster tank is good for the fish. The owner yeah, the fish no. Also piss poor surface beneficial bacteria.
Silk floating vines work. U can also paint/cover the sides. Sand. Smooth stones at the bottom. It can be done easily. More glass equals more reflections/shadows to spook at. Another trick is to silicone filter foam on the sides and back. Gives padding, looks good and has great bacterial surface.