1. Install forge 47.3.1
2. Download embeddium-0.3.20, modernfix 5.18.1, dynamiclightsreforged-1.20.1_v1.6.0, BadOptimizations
3. In the settings put Slow or Fast
4. On my server, the torch in my hand almost immediately stopped shining.

Could probably be fixed by turning off lightmap optimizations in the config but just curious, which of those mods makes the torch shiny?

https://www.curseforge.com/minecraft/mc-mods/dynamiclights-reforged

Does turning off lightmap caching in the config fix it?

No

My next guess is entity data optimizations? If that doesn't work you could just keep disabling each one until it works.

I think something is useless to fix

This is a photo without your mod. In any case, if you use the Realtime settings, then everything works correctly, even with Badoptimizations

So...issue fixed, or?

I'll test the realtime a little and close it