Crimson Fungi and Warped Fungi can only be bone-mealed on their respective nyliums (crimson, warped). i.e., Crimson fungi can be placed on both crimson and warped nylium, but only bone-mealed on crimson nylium. Warped fungi can be placed on both crimson and warped nylium, but only bone-mealed on warped nylium. This is true in both the nether and overworld.

If this is intentional, then ignore this. However, it might make more sense for either warped things to not be place-able on crimson things and vice versa, or everything be able to be placed (and bone-mealed) on everything else.

Thank you!