In the Entities sprite, at the bottom there are three important scripts: Animations, Movement, and Is Shot. If you take out Animations and Movement from the clone's forever loop, then shooting takes away the enemy's health, but if those scripts are running, then Is Shot seemingly is overridden or doesn't have enough time to run.

I haven't added a proper controls HUD, but
Shooting is Spacebar,
Opening Doors (The first room has a door) is F,
WASD to move
mouse to (badly) look around.

https://scratch.mit.edu/projects/891977166

If you move the other scripts to different threads they will all run independently, which will let the the damage code run uninterrupted.