Summary:
Blocks requiring support can be placed on the top side of the Hopper (lantern, bell, torch...). Since the top side is incomplete, it should not contain almost any blocks that require support, as is done in Java (except for Signs, Pressure Plate, Sea Pickles...).

Here is a comparison of the main blocks:

Block	Bedrock	Java
Sea Pickles
Pressure Plates
Redstone
Redstone Repeater/ Comparator
Rails
Bell
Scaffolding
Levers
Glow Lichen/ Sculck Vein
Amethyst Cluster
Buttons
Pointed Dripstone
Snow
Doors
Corals
Torchs
Lanterns
Candles

Steps to reproduce:

1. Place Hopper.
2. Place blocks like torch, lantern, redstone, bell... on the top side.

Observed results:
Blocks can be placed on the top side.

Expected results:
The top side is incomplete, so no blocks will be placed on it.