On 1.20.1, I am using Appleskin. If relevant, I am also using Dragon Survival. It appeared that the mod was not functioning, but it appears that it is being rendered BELOW the screen. In the screenshot, you can see the hearts overlay peeking up a little bit.

Very likely to be a mod compatibility problem.

Forge/NeoForge or Fabric? Any other mods installed?

I am on 1.20.1, Forge, and I have a total of 144 mods.

I would suggest something like an offset mode? I'm not sure what would help but it's definitely a decent bandaid patch