I am playing on Java Edition; version 1.12.2, not 1.16.4!!
According to this Minecraft-Wiki link, I should get 1-XP when melting/burning a cactus in a furnace.
But in reality you only get between 0.1875 and 0.2 XP from one melted or burned cactus.
You can try this in singeplayer as well as on multiplayer servers.
After trying different Minecraft versions, this problem is "fixed" in version 1.13 and only appears in version 1.12.2 and older ones.
Could you please fix this? There is a lot of experience I am missing because of this
Thank you very much!