As of 1.18, mobs need complete darkness to spawn. It would be nice if the default option from version 1.18 would be set to 0 because now if people won't change it themselves it will spread misinformation.

Install modmenu too and you can configure the X to only appear on level 0. Im using it on fabric. I had to change yellow X to red too, but its working well.
https://www.curseforge.com/minecraft/mc-mods/modmenu

I know, I already did it, but my point is that it shouldn't be necessity.

Like, is right for an informative mod to show wrong information by default?

And just because it is possible for change shouldn't mean that every user needs to also download another mod if they don't have it already and change that value manually, some people don't know that this mod shows wrong information and there are others who doesn't know that it was changed in Minecraft at all etc.

Thanks for the feedback, a blue cross will now be displayed for spawners, while the old yellow cross will be light level 0 at night, and red cross be always spawning