Cinnamon in Coffee ?

Put it in your coffee once it is in your mug.

^Same answer.
Cinnamon is probably too thick for the filters
Here is a link that talks about how to clean a Keurig. My apologies for it not talking about how to clean a Keurig specifically if it’s clogged with cinnamon.

Keurig sells their own brand of coffee cleaner, but Bed Bath and Beyond sells a cheaper product that works as well, and they guarantee it will not damage a Keurig.

I’m thinking that the cinnamon swells up when it’s been wet for a while. That may affect how easy it is to remove it.

Try cinnamon sticks.