Steps to reproduce:
1. Get a map
2. Spawn a zombie
3. /effect give @e[type=zombie,distance=..3] minecraft:glowing
This effects all entites, not just zombies.
Linked issues
Attachments
Comments 6
Since the glowing effect does render behind the hotbar, I guess it is supposed to render behind other HUD elements as well.
Items carried in your hand are not a part of the user interface, thus glowing effects should show through them.
Can Confirm for Minecraft 19w40a