The component minecraft:fuel doesn't work, it doesn't allow you to place the item in the fuel slot in a furnace.
To reproduce it you must create a new item with the component minecraft:fuel and then try it out. What should happen with it is that the item is used up and fuels the furnace with the set duration it was given.
Thank you for your report!
We're actually already tracking this issue at MCPE-102400, so I will resolve and link this ticket as a duplicate.
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