This should work with any plant. It is going to depend on how much cinnamon you use however, and the severity of the fungus you are trying to kill off.

If you have fungus in your houseplants, there may be another issue causing it, such as overwatering, poor soil, compacted soil, compacted roots, poor quality fertilizer, etc....

What is the problem with your houseplants you are trying to fix?

Let us know how it works for ya. If you have a lot of seedlings, maybe try different concentrations of the cinnamon if you can afford to experiment with it. I would say trying less is better until you see how it works.

Something else to keep in mind if you think the mix is too strong is to strain it thru a cheeseclothe to get the cinnamon granules out of the water mix. That will make it a bit weaker and you can also dilute it with more warm water if you think it's still too strong for your seedlings.