In 1.19.40, the light block graphic will be invisible when a player holds a light block. You can only see them via outline. You can still interact with them as normal.
However, if you hold a barrier, the light blocks will appear. Players cannot interact with the light blocks while holding barriers, only view them.

Steps to reproduce:
1: Place a light block
2: Hold a light block
3: Observe that you cannot see the light block.
Alternatively:
1: Place a light block
2: Hold a barrier
3: Observe that you can see the light block.