The game will tell you if your oponent is too heavy to throw and inspecting him doesnt make him any lighter.
After you commit to the move. It’s a turn based game, you need to be able to make decisions before you make a move. Even seeing a weight would be problematic - it is easier to remember that I can throw goblin without a buff, and human with a buff, rather then trying to remember how strength corresponds to stones, or whatever weight measurement BG3 is using.
