This is just a mod development guide. If possible, can you add a glowing cloak feature?

ah not adjust brightness but make the cloak glow in the night, features include:
glowing_mode:true/false
light intensity:value

Not really sure what you mean? Like set the brightness to max the entire time?

? Thats what the glow is. Entities on fire/Spider eyes/enderman eyes are just rendered with 15 brightness.

No no, I mean add a feature that makes the cloak glow in the dark, naturally.

For example, when in the dark, the cape will be dark, but there is an additional feature that makes the cape brighter.

Ah yea no. That would require rendering the cape twice, and have custom capes with 2 textures. This mod doesn't add capes, and there is no mod providing capes with textures like that.

Also the word you are looking for is "Emissive textures"

Oh, I see, okay thank you very much