Health + Shield in one progress bar

I would just use the “overlay” option. Create 2 progress bars, health first then shield so shield is always drawn last and over the health bar. In the shield’s background style options, go to tint, set the alpha to 0. You now have 2 overlaid bars when the shield depletes it will reveal the health bar below. Each can be independently controlled with code/script to function however you like in your game.