With modpacks that lack Optifine and use Magnesium (or Halogen) many features such as emissive textures don't work.
Indium normally fixes many of these in Fabric.

An Indium Forge port built as an addon for Magnesium would resolve this issue for Magnesium related modpacks that are unable to use Optifine.

This would go great alongside Lilac the Iris forge port.

Indium:
https://www.curseforge.com/minecraft/mc-mods/indium

Indium bridges Sodium with the Fabric Rendering API, which is what adds those features, AFAIK. It would do nothing on Forge.