on a multiplayer vanilla server, you cannot smelt anything with any furnace. In singleplayer mode, you can smelt. 

What I expected to happen was:
The furnace would smelt the items I put in it. 

What actually happened was:
Nothing. The furnace would not smelt items and wouldn't put the ingredients in when I used the crafting/smelting menu. 

Steps to Reproduce:
1. Download and run a multiplayer server on 21w14a. Join the server. 
2. Try to smelt something such as raw meat or raw iron. It wont smelt. 
3. Repeat in singleplayer mode. It will smelt. 

edit: its a different bug than I thought and its actually most likely MC-215909 as I restarted the server and smelting works again.