I'm not sure if this is a bug or not; when enabling the burnable fuel option it disables/removes nutrients as fuel completely.

Definitely not intentional; I wonder if this was a base game change, or maybe caused by another mod, but I'll look into this later today, thanks!

Just tested this with only space age, and then with All Planets Lite, and nutrients are allowed whether or not the setting is enabled.

There might be another mod affecting things, either removing its fuel value, or removing it from the "chemical" fuel category, or modifying the nutrient inserter directly? Not sure what could be happening, but I do suspect it's caused by a third-party mod

Ok, I'll do some testing with the mods I'm running. I'll return once i figure out what's causing it.

Amator Phasma's coal and steam (forked) causes the issue