If you try and smelt the wart or crimson stems in 20w06a they don't smelt and don't turn into charcoal, I don't know if this was an intended game design or not.
MC-171693
Crimson and warped stems cannot be turned into charcoal
Resolved
Works As Intended
3
Without correcting this oversight, there is no way at all to obtain the low-level ingredient coal/charcoal in the Nether if the game is set to Peaceful mode. It's also a bit extreme to expect people to hunt wither skeletons to obtain basic materials.