is cinnamon powder the same as ground cinnamon

Yes — cinnamon powder and ground cinnamon are the same thing.

Both terms refer to cinnamon bark that has been dried and finely ground into a powder. The difference is simply in wording:

“Ground cinnamon” is the more traditional term
“Cinnamon powder” is often used in retail and online listings
In practice: they are interchangeable and can be used in exactly the same way in food, drinks, or as part of a supplement routine.